Code Modernization: Explicitly declare all properties in various tests.

Dynamic (non-explicitly declared) properties are deprecated as of PHP 8.2 and are expected to become a fatal error in PHP 9.0.

In each of the cases included in this commit, one or more individual tests set a property to allow a filter or action access to certain information.

This commit:
* Explicitly declares these properties and documents in which tests they are being used.
* Adds a reset to the default value of the property to a pre-existing `tear_down()` method or adds that method specifically for that purpose. This ensures that tests do not accidentally “taint” each other.

As these properties are being declared on test classes, they are marked as private. Even though the original dynamic property was public, this should not be considered a backward compatibility break as this only involves test classes.

Includes:
* In the `Tests_Post_Query` class, there were two tests assigning a value to an undeclared `$post_id` property, but subsequently not using the property, so those assignments should have been to a local variable (if they should be assignments at all).
* In the `Test_User_Capabilities` class, the property name had a leading `_` underscore. This is an outdated PHP 4 practice to indicate a private property. As PHP 4 is no longer supported, the leading underscore is removed from the property name.
* In the `Tests_User_Capabilities` class, an unused `$_role_test_wp_roles_role` property was declared somewhere in the middle of the class. That property is now removed in favor of `$_role_test_wp_roles_init`, which appears to be the intended name, previously misspelled.

Follow-up to [27294], [36277], [36750], [37712], [38571], [39082], [40290], [43049], [44628], [48328], [53557], [53558], [53850], [53851], [53852], [53853], [53854], [53856], [53916], [53935], [53936], [53937], [53938].

Props jrf.
See #56033.
Built from https://develop.svn.wordpress.org/trunk@53942


git-svn-id: http://core.svn.wordpress.org/trunk@53501 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53941';
+$wp_version = '6.1-alpha-53942';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.