Improve WP_Term's sanitization calls

[Cybr]

Akin to WP_Post::filter(), I think WP_Term::filter() should have a bypass, too. This will significantly improve performance wherever terms are used (list edit screens, category widgets, blocks) because the bypass prevents redundant re-sanitization.

The attached patch will shave off a 30% load time at wp-admin/edit.php after #50567's implementation. This patch tests for the WP_Term object's ::$filter state, and only re-sanitizes the term when the state differs from the input argument.

You'll also find that sanitize_term() now looks a lot like sanitize_post()--the same goes for get_term()'s resemblance to get_post(). Overall, it seems posts have received a lot more love over the years, and this patch steals some of that.

There are a few issues with terms, however. For example, update_term_cache() caches terms regardless of being shared, while WP_Term::get_instance() tries to prevent that. The $filter = 'display' argument is used in contexts where raw would do fine, too (e.g. @ WP_Terms_List_Table::single_row()). If we iron those issues out, we can fully phase out the re-sanitization of terms.

[hellofromTonya]

From today's 5.6 core scrub, Sergey:

This could probably use some unit tests. Both #50567 and this one are nice performance enhancements, but also seem like early tickets, should probably be moved to 5.7.

Moving this ticket to early 5.7 milestone along with #50567.

If any maintainer or committer feels this can be resolved in time, or wishes to assume ownership during a specific cycle, feel free to update the milestone accordingly.

[hellofromTonya]

This ticket is marked for early in the alpha cycle. We are now in the Beta cycle and long past early. Moving this ticket and #50567 to Future Release. However, would be great to get both committed early in 5.8 alpha cycle if possible.

If any maintainer or committer feels this can be resolved in time, or wishes to assume ownership during a specific cycle, feel free to update the milestone accordingly.