KSES: Reimplement with Tag Processor

[dmsnell]

Trac ticket: Core-65984

Merge after #13273, which accounts for three of the failing tests.

• self-closing non-HTML elements
• [~] remove opening tag when required attributes are missing, and closing tag
  • while this would be a nice enhancement it’s going to be left out of this work to preserve existing behaviors. with the HTML Processor powering wp_kses(), it’s possible to simply wait until an opened element is closed based on depth, and skip that closing element if it exists.
• replace C0 controls with their escapes, rather than stripping them away
• [~] handle incomplete parsing, including closing all open elements
  • plenty of existing code in Core calls wp_kses() with intentionally-incomplete input, for example, a wrapper opening tag with part of the content, separately from the closer. closing open elements does a good job of isolating content, but legacy behaviors depend too much on the more procedural use of wp_kses() so isolation cannot be reasonably added without mangling websites.

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