feature request: warn about possibly undefined symbols

[azjezz]

some symbols can be conditionally defined in PHP, such as those defined within another symbol, or inside a conditional statement ( e.g if ).

Psalm should give a warning about using such symbols.

https://psalm.dev/r/1bc794cbb3

PHPStan handles this properly by emitting an erorr: https://phpstan.org/r/1c264348-8f9a-41b7-854b-b08e9148c67c

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1bc794cbb3

<?php

if (PHP_VERSION == 80) {
    function biz(): void {
    }
}

function foo(): void {
    function bar(): void {
        class Baz {
            
        }
    }
    
    bar();
}

biz();

bar();

new Baz();

Psalm output (using commit dee5fe4):

No issues!