Avoid defining block body and expression body multiple times

Even though the precise context for the original definitions isn't
applicable other times, it's simpler to just leave those as the sole
definitions. The other uses are conceptually equivalent - it's not
like we're actually defining different terms.

Additionally, replace "statement body" with "block body" for both
properties and indexers.

Fixes dotnet#948.
Fixes dotnet#877.

standard/classes.md

@@ -2027,7 +2027,7 @@ For abstract and extern methods, the *method_body* consists simply of a semicolo
 
 If the *method_body* consists of a semicolon, the declaration shall not include the `async` modifier.
 
-The *ref_method_body* of a returns-by-ref method is either a semicolon, a ***block body*** or an ***expression body***. A block body consists of a *block*, which specifies the statements to execute when the method is invoked. An expression body consists of `=>`, followed by `ref`, a *variable_reference*, and a semicolon, and denotes a single *variable_reference* to evaluate when the method is invoked.
+The *ref_method_body* of a returns-by-ref method is either a semicolon, a block body or an expression body. A block body consists of a *block*, which specifies the statements to execute when the method is invoked. An expression body consists of `=>`, followed by `ref`, a *variable_reference*, and a semicolon, and denotes a single *variable_reference* to evaluate when the method is invoked.
 
 For abstract and extern methods, the *ref_method_body* consists simply of a semicolon; for all other methods, the *ref_method_body* is either a block body or an expression body.
 
@@ -3168,15 +3168,15 @@ The *member_name* ([§15.6.1](classes.md#1561-general)) specifies the name of th
 
 The *type* of a property shall be at least as accessible as the property itself ([§7.5.5](basic-concepts.md#755-accessibility-constraints)).
 
-A *property_body* may either consist of a ***statement body*** or an ***expression body***. In a statement body,  *accessor_declarations*, which shall be enclosed in “`{`” and “`}`” tokens, declare the accessors ([§15.7.3](classes.md#1573-accessors)) of the property. The accessors specify the executable statements associated with reading and writing the property.
+A *property_body* may either consist of a block body or an expression body. In a block body, *accessor_declarations*, which shall be enclosed in “`{`” and “`}`” tokens, declare the accessors ([§15.7.3](classes.md#1573-accessors)) of the property. The accessors specify the executable statements associated with reading and writing the property.
 
-In a *property_body* an expression body consisting of `=>` followed by an *expression* `E` and a semicolon is exactly equivalent to the statement body `{ get { return E; } }`, and can therefore only be used to specify read-only properties where the result of the get accessor is given by a single expression.
+In a *property_body* an expression body consisting of `=>` followed by an *expression* `E` and a semicolon is exactly equivalent to the block body `{ get { return E; } }`, and can therefore only be used to specify read-only properties where the result of the get accessor is given by a single expression.
 
 A *property_initializer* may only be given for an automatically implemented property ([§15.7.4](classes.md#1574-automatically-implemented-properties)), and causes the initialization of the underlying field of such properties with the value given by the *expression*.
 
-A *ref_property_body* may either consist of a statement body or an expression body. In a statement body a *get_accessor_declaration* declares the get accessor ([§15.7.3](classes.md#1573-accessors)) of the property. The accessor specifies the executable statements associated with reading the property.
+A *ref_property_body* may either consist of a block body or an expression body. In a block body a *get_accessor_declaration* declares the get accessor ([§15.7.3](classes.md#1573-accessors)) of the property. The accessor specifies the executable statements associated with reading the property.
 
-In a *ref_property_body* an expression body consisting of `=>` followed by `ref`, a *variable_reference* `V` and a semicolon is exactly equivalent to the statement body `{ get { return ref V; } }`.
+In a *ref_property_body* an expression body consisting of `=>` followed by `ref`, a *variable_reference* `V` and a semicolon is exactly equivalent to the block body `{ get { return ref V; } }`.
 
 > *Note*: Even though the syntax for accessing a property is the same as that for a field, a property is not classified as a variable. Thus, it is not possible to pass a property as an `in`, `out`, or `ref` argument unless the property is ref-valued and therefore returns a variable reference ([§9.7](variables.md#97-reference-variables-and-returns)). *end note*
 
@@ -4198,13 +4198,13 @@ The *formal_parameter_list* specifies the parameters of the indexer. The formal
 
 The *type* of an indexer and each of the types referenced in the *formal_parameter_list* shall be at least as accessible as the indexer itself ([§7.5.5](basic-concepts.md#755-accessibility-constraints)).
 
-An *indexer_body* may either consist of a statement body ([§15.7.1](classes.md#1571-general)) or an expression body ([§15.6.1](classes.md#1561-general)). In a statement body, *accessor_declarations*, which shall be enclosed in “`{`” and “`}`” tokens, declare the accessors ([§15.7.3](classes.md#1573-accessors)) of the indexer. The accessors specify the executable statements associated with reading and writing indexer elements.
+An *indexer_body* may either consist of a block body ([§15.7.1](classes.md#1571-general)) or an expression body ([§15.6.1](classes.md#1561-general)). In a block body, *accessor_declarations*, which shall be enclosed in “`{`” and “`}`” tokens, declare the accessors ([§15.7.3](classes.md#1573-accessors)) of the indexer. The accessors specify the executable statements associated with reading and writing indexer elements.
 
-In a *indexer_body* an expression body consisting of “`=>`” followed by an expression `E` and a semicolon is exactly equivalent to the statement body `{ get { return E; } }`, and can therefore only be used to specify read-only indexers where the result of the get accessor is given by a single expression.
+In a *indexer_body* an expression body consisting of “`=>`” followed by an expression `E` and a semicolon is exactly equivalent to the block body `{ get { return E; } }`, and can therefore only be used to specify read-only indexers where the result of the get accessor is given by a single expression.
 
-A *ref_indexer_body* may either consist of a statement body or an expression body. In a statement body a *get_accessor_declaration* declares the get accessor ([§15.7.3](classes.md#1573-accessors)) of the property. The accessor specifies the executable statements associated with reading the property.
+A *ref_indexer_body* may either consist of a block body or an expression body. In a block body a *get_accessor_declaration* declares the get accessor ([§15.7.3](classes.md#1573-accessors)) of the property. The accessor specifies the executable statements associated with reading the property.
 
-In a *ref_indexer_body* an expression body consisting of `=>` followed by `ref`, a *variable_reference* `V` and a semicolon is exactly equivalent to the statement body `{ get { return ref V; } }`.
+In a *ref_indexer_body* an expression body consisting of `=>` followed by `ref`, a *variable_reference* `V` and a semicolon is exactly equivalent to the block body `{ get { return ref V; } }`.
 
 > *Note*: Even though the syntax for accessing an indexer element is the same as that for an array element, an indexer element is not classified as a variable. Thus, it is not possible to pass an indexer element as an `in`, `out`, or `ref` argument unless the indexer is ref-valued and therefore returns a reference ([§9.7](variables.md#97-reference-variables-and-returns)). *end note*