Tests: Combine test classes for `get_edit_term_link()` tests.

There were two sets of tests for the function:
* One in the `link` directory, based on the `link-template.php` file name.
* One in the `term` directory, based on the component name.

To avoid confusion and make it easier to decide where new tests should go in the future, the existing tests are now combined in the former location.

Includes:
* Setting the current user in `::set_up()` instead of each individual test method.
* Changing the custom taxonomy name to `wptests_tax` for consistency with other tests.
* Moving `::register_custom_taxonomy()` and `::get_term()` helpers to the beginning of the class.

Follow-up to [32954], [36646], [52180], [52255], [53833].

See #55652.
Built from https://develop.svn.wordpress.org/trunk@53836


git-svn-id: http://core.svn.wordpress.org/trunk@53395 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53835';
+$wp_version = '6.1-alpha-53836';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.