Detect `while`/`until`/`repeat` loops that could be replaced with `foreach`

[byakuren-hijiri]

It is possible to find while/until/repeat loops that could be safely replaced to foreach.

If the loop condition variable is increasing and only using to access a map element, we should suggest replacing the entire loop with foreach:

let m: map<Int, Int>;
let mSize: Int;

fun test() {
    let i: Int = 0;
    while (i < self.mSize) {
        i = i + 1;
        dump(self.m.get(i));
    }
}

Could be replaced with:

let m: map<Int, Int>;
let mSize: Int;

fun test() {
    let i: Int = 0;
    foreach (_k, v in self.m) {
        dump(v);
    }
}

Things to consider:

• The condition variable should be limited by the size of the map. However, there is no .size or .length operation in Tact maps. Therefore, we cannot be 100% sure if the user intended to iterate the whole map there.
• We should have types in AST nodes first, which requires the updated type checker in the compiler (#70)

[jubnzv]

Depends on #70