Fix bug with type aliases to structs

@max-melentyev found in #843 that type aliases to structs were being
rendered as a struct literal. The problem was that we need the type of the
right hand side of the alias definition, not the underlying type itself.

.mockery.yaml

@@ -108,4 +108,10 @@ packages:
             mockname: InterfaceWithUnresolvedAlias
           - resolve-type-alias: True
             mockname: InterfaceWithResolvedAlias
+      Interface2:
+        configs:
+          - resolve-type-alias: False
+            mockname: Interface2WithUnresolvedAlias
+          - resolve-type-alias: True
+            mockname: Interface2WithResolvedAlias
 

pkg/fixtures/type_alias/interface.go

@@ -1,7 +1,14 @@
 package type_alias
 
+import "github.com/vektra/mockery/v2/pkg/fixtures/type_alias/subpkg"
+
 type Type = int
+type S = subpkg.S
 
 type Interface1 interface {
 	Foo() Type
 }
+
+type Interface2 interface {
+	F(Type, S, subpkg.S)
+}

pkg/fixtures/type_alias/interface_test.go

@@ -25,6 +25,11 @@ func TestTypeAlias(t *testing.T) {
 			filepath:      "./mock_InterfaceWithUnresolvedAlias_test.go",
 			expectedRegex: `func \((_?[a-zA-Z]*)+ \*InterfaceWithUnresolvedAlias\) Foo\(\) type_alias.Type {`,
 		},
+		{
+			name:          "Alias to type with underlying struct with resolve-type-alias: True",
+			filepath:      "./mock_Interface2WithResolvedAlias_test.go",
+			expectedRegex: `func \(_m \*Interface2WithResolvedAlias\) F\(_a0 int, _a1 subpkg.S, _a2 subpkg.S\) {`,
+		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
 			regex, err := regexp.Compile(tt.expectedRegex)

pkg/fixtures/type_alias/subpkg/interface.go

@@ -0,0 +1,5 @@
+package subpkg
+
+type S struct {
+	A int
+}

pkg/generator.go

@@ -547,8 +547,7 @@ func (g *Generator) renderType(ctx context.Context, typ types.Type) string {
 					"url": logging.DocsURL("/deprecations/#resolve-type-alias"),
 				},
 			)
-			log.Debug().Msg("resolving type alias to underlying type")
-			return g.renderType(ctx, t.Underlying())
+			return g.renderType(ctx, t.Rhs())
 		}
 		log.Debug().Msg("not resolving type alias to underlying type")
 		return g.renderNamedType(ctx, t)