Docs: Update code examples formatting in `WP_HTML_Tag_Processor` documentation.
Per the [https://developer.wordpress.org/coding-standards/inline-documentation-standards/php/#description documentation standards], code samples should be created by indenting every line of the code by 4 spaces, with a blank line before and after. This matches the format used by the rest of core.
Follow-up to [55203], [55304], [55718], [55724].
Props juanmaguitar, coffee2code, azaozz, costdev, dmsnell, johnbillion, SergeyBiryukov.
Fixes #58028.
Built from https://develop.svn.wordpress.org/trunk@55727
git-svn-id: http://core.svn.wordpress.org/trunk@55239 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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