This PR:

• adds support for arrays in the Leo language.
• introduces the TypeTable, which tracks the types of expressions across the AST passes.
• refactors tuple destructuring out of the flattening pass.

Arrays

• Arrays must be static.
• Arrays only support constant accesses (the index must be a constant value).
• Arrays can be accessed by any constant integer.
• Arrays can contain primitive data types, structs, or arrays.
• Structs and records can contain arrays.
• Arrays can be initialized via an array expression, e.g [a, b, c, d]
• Arrays cannot be empty.
• Arrays cannot be modified.

Let's look at some example code.

program test.aleo {
    transition sum_with_loop(a: [u64; 4]) -> u64 {
        let sum: u64 = 0u64;
        for i: u8 in 0u8..4u8 {
            sum += a[i];
        }
        return sum;
    }
}

This function takes in an array as input and returns the sum of its elements.
Note that array types can be declared as [<element_type>; <nonzero_number>]