HTML Processor: Increase MAX_BOOKMARKS

[sirreal]

Bookmark exhaustion has been observed on fairly standard WordPress post content. This is partially related to WordPress/gutenberg#70542 which may nest formatting elements to extreme depths.

The initial limit of 100 bookmarks was very conservative. A significant increase in bookmarks seems to perform well without excessive memory usage.

Related to #10616.

Trac ticket: https://core.trac.wordpress.org/ticket/64394

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[github-actions]

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[dmsnell]

In my own testing I found that 3,000 was sufficient to parse all but the most extreme documents, and 6,000 I believe was sufficient to parse the home page of the 300,000 most-visited domains.

[github-actions]

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