[Bug][move-compiler-v2] Move language <= 2.1 has separate function and variable namespaces

[brmataptos]

🐛 Bug

This is related to #15360, but different. It's a well-defined semantics, but probably not what we want in a language with function values.

The Move language (through Move 2.1) has separate name spaces for function names and variables.

Consider the following program:

module 0x42::Test {

    public fun f(a: u64, b: u64): u64 {
        a * b
    }

    public fun test_shadowing(): u64 {
        let f = 7;
        f(3, 4) + f
    }
}

Note that there is both a local variable f and visible function f in the body of test_shadowing(). In the function call position preceding (...), the name f refers to the function. In other expressions, f refers to the local variable.

The historic distinction between "Lisp 2" and "Lisp 1" isn't seeming so strange all of a sudden.