This commit renames the `$tag` and `$function_to_add` parameters to match the `add_filter()` function signature.
Includes:
* Renaming the `$tag` parameter to `$hook_name`.
* Renaming the `$function_to_add` parameter to `$callback`.
* Synchronizing documentation for:
* `tests_add_filter()` and `add_filter()`
* `_test_filter_build_unique_id()` and `_wp_filter_build_unique_id()`
Follow-up to [760/tests], [38582], [43555], [46801], [50807], [52300], [53804], [53805], [55023].
See #56793.
git-svn-id: https://develop.svn.wordpress.org/trunk@55025 602fd350-edb4-49c9-b593-d223f7449a82
e088de67e8