PHPStan: Fix function argument type issues for WP 6.4

[hellofromTonya]

Previously:

• #57782 (6.3)
• #51423 (<= 6.2)

Continuation of the the work to fix function argument type issues as reported by PHPStan. These issues are argument types passed to a WP Core and PHP's built-in functions.

The last report was created 3 years ago ​https://gist.github.com/xknown/77f8cbe233da75080d1e9258a8c94f95. A new report should be generated as a starting point what issues remain to be fixed in 6.3.

Goals are to:

• retain the current behavior (i.e. to avoid breaking changes).
• retain the triggering of notice/warning/error, which are clues and indicators (i.e. rather than silently letting the problem propagate downstream).
• gain PHP 8 compatibility.
• ensure code coverage to validate changes.

This ticket is part of the effort to achieve PHP 8+ compatibility.

[hellofromTonya]

This ticket is not tracking PHP 8+ incompatibilities, thus the php-compatibility focus is not added. Rather, this ticket is an effort of analyzing PHPScan "function argument type issues" and when needed, add defensive code improvements.

[hellofromTonya]

6.4 RC1 is in a couple of hours. #59653 is now open for 6.5.