Fix: Bug in _get_wptexturize_split_regex and get_html_split_regex

[nickchomey]

There was an error in the regex used in _get_wptexturize_split_regex() and get_html_split_regex().

As shown in the associated trac ticket, if an HTML attribute contained >, the old regex treated it as the closing > for the element — the pattern [^>]*> simply consumed everything up to the first > character.

The new regex (?:"[^"]*"|'[^']*'|[^>])*+>? places quoted attribute values before the generic character matcher, so "..." and '...' spans are consumed as atomic units - any > inside them is absorbed into the value rather than terminating the tag. The generic [^>] at the end acts as a catch-all for everything else (tag names, unquoted attributes, malformed fragments like <'word), and the possessive *+ on the outer group prevents backtracking issues.

Trac tickets:
https://core.trac.wordpress.org/ticket/63997
https://core.trac.wordpress.org/ticket/57381
https://core.trac.wordpress.org/ticket/43785
https://core.trac.wordpress.org/ticket/63426

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Used for: Diagnosis and implementation of fix. I reviewed and tested it.

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[nickchomey]

I made another commit that modified the regex a bit further (?:"[^"]*"|\'[^\']*\'|[^<>])*+> in order to handle the edge case in https://core.trac.wordpress.org/ticket/43785. It required some other test cases to change though, but I dont think it matters - it now texturizes invalid html/content.

[nickchomey]

Also took the liberty of addressing a TODO comment in _get_wptexturize_split_regex to replace it with get_html_split_regex(). All tests still pass.