[php-src] Issue #7845: Stop to automatically cast numeric-string to int when using them as array-key

Issue: https://github.com/php/php-src/issues/7845 Comment Author: iluuu1994 Basically, this behavior is there to [0 => 'foo']/['0' => 'foo'] and $array[0]/$array['0'] equivalent. Even if it's possible to persist the key types while keeping this behavior the same, any change in arrays will likely lead to countless subtle bugs in countless PHP code bases. There's also no good migration path to make users aware of this chance.