Docs: Replace short array syntax in `WP_HTML_Tag_Processor` documentation.
Per [https://developer.wordpress.org/coding-standards/wordpress-coding-standards/php/#declaring-arrays WordPress PHP Coding Standards]:
> Using long array syntax ( `array( 1, 2, 3 )` ) for declaring arrays is generally more readable than short array syntax ( `[ 1, 2, 3 ]` ), particularly for those with vision difficulties. Additionally, it’s much more descriptive for beginners.
>
> Arrays must be declared using long array syntax.
Original PR from Gutenberg repository:
* [https://github.com/WordPress/gutenberg/pull/47958 #47958 Docs: Don't recommend using short array syntax in WP_HTML_Tag_Processor]
Follow-up to [55203], [55206].
Props aristath, poena.
Fixes #57691.
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