Fix code issues identified by PHPStan

[johnbillion]

In #51423 several issues were identified with function argument types that were detected by PHPStan.

There are other issues that PHPStan detects too such as potentially undefined variables, functions called with incorrect number of parameters, access to undefined properties, and more as you increase the level of checking performed.

We can scan core using the level 1 checks and catch quite a few low hanging fruit, and then go from there.

Follow-up task: Consider whether it's beneficial to add PHPStan (or Psalm or Phan) analysis to the build tooling and CI.

Trac ticket: https://core.trac.wordpress.org/ticket/52217

This introduces config for PHPStan with plenty of exclusions so we can identify real issues that need to be fixed.

[jorbin]

Left one comment about where we put the bootstrap file, otherwise, love this idea.

Consider whether it's beneficial to add PHPStan (or Psalm or Phan) analysis to the build tooling and CI.

I lean towards yes

[szepe.viktor]

to add PHPStan (or Psalm or Phan) analysis to the build tooling and CI.

Let's lean towards PHPStan.

written by a PHPStan Advocate

[johnbillion]

In 49936:

Docs: Corrections and improvements to types used in various docblocks.

See #51800, #52217

[johnbillion]

In 49946:

Plugins: Replace usage of $this in action and filter parameter docblocks with more appropriate variable names.

See #51800, #52217

Fixes #52243