In `wptexturize()` + tests:
* Allow well-formed HTML inside of shortcode attributes
* Restrict recursion. HTML is allowed but ignored.
* Do not allow exotic HTML comments in shortcode attributes.
* Continue to ignore the [ and ] chars if they appear in any HTML attribute.
* Update related regex patterns.
* Update unit tests.

Props miqrogroove.
Fixes #28564.


git-svn-id: https://develop.svn.wordpress.org/trunk@28773 602fd350-edb4-49c9-b593-d223f7449a82