HTML API: Backport from Gutenberg of layout image container refactor.

[dmsnell]

Trac ticket: Core-63694.
See WordPress/gutenberg#72264.

For classic themes, image blocks need to create a DIV wrapper which contains alignment classes from the inner FIGURE. This has been processed using PCRE matching.

With this change the HTML API is used instead of PCRE functions to provide more semantic transformation, clearer intent, and eliminate possible parsing issues.

[github-actions]

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[github-actions]

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