forbid trivial local address returned from functions

[andrewrk]

progress towards #25312 (I amended the proposal to include more cases)

Upgrade Guide

fn foo() *i32 {
    var x: i32 = 1234;
    return &x;
}

test.zig:3:13: error: returning address of expired local variable 'x'
    return &x;
            ^
test.zig:2:9: note: declared runtime-known here
    var x: i32 = 1234;
        ^

⬇️

fn foo() *i32 {
    return undefined;
}