Rename `$this` when used in `@param` tags

[johnbillion]

Several filters and actions pass $this as a parameter. $this is a pseudo-variable that cannot be used as the name of a function parameter.

I've identified a few problems caused by using $this as the name of a parameter for actions and filters:

• Inexperienced developers may copy and paste the list of parameters from the apply_filters() call or from the developer.wordpress.org site when adding their filter and then experience a fatal error
• Developer tools that consume filter and action docblocks, for example code generators, have to rename $this to avoid the same
• PHPStan and other static analysis tools report $this as invalid when used in a @param tag

Usage of $this in @param tags for actions and filters should be replaced with a more appropriate variable name.

[audrasjb]

Hi John, great point!

Maybe we may also want to provide more descriptive params for functions/hooks that are passing $array.
I found few occurrences, for example:

In class-requests.php

/**
 * Convert a key => value array to a 'key: value' array for headers
 *
 * @param array $array Dictionary of header values
 * @return string[] List of headers
 */
public static function flatten($array) {

Or maybe you'll prefer this to be another ticket :)

[johnbillion]

Yes that's a good idea too. Can you open another ticket please?

[audrasjb]

Sure!

[johnbillion]

In 49946:

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

See #51800, #52217

Fixes #52243