HTML API: Refactor wp_kses_hair()

[dmsnell]

Trac ticket: Core-63694

Replaces #7407, dmsnell#5
Coordination in #9256

wp_kses_hair() is built around an impressive state machine for parsing the $attr of an HTML tag, that is, the span of text after the tag name and before the closing >. Unfortunately, that parsing code doesn’t fully-implement the HTML specification and may be prone to mis-parsing.

This patch replaces the existing state machine with a straight-forward use of the HTML API to parse the attributes for us, constructing a shell take for the $attr string and reading the attributes structurally. This shell is necessary because a previous stage of the pipeline has already separated what it thinks is the so-called “attribute list” from a tag.

Dependencies

• HTML API: Use Tag Processor when adding rel keywords to A elements. #9252
  • HTML API: Use assertEqualHTML() in wp_rel_nofollow() tests. #9251
  • HTML API: Use assertEqualHTML in wp_rel_ugc() tests. #9255
• HTML API: Use assertEqualHTML() in wp_kses() tests. #9257
• HTML API: Use assertEqualHTML() in post filtering tests. #9258
• HTML API: Rely on HTML API in oEmbed filtering tests. #9259
• HTML API: Use assertEqualHTML() in media tests. #9264

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