Convert emojies to HTML entities for utf8mb3 columns during wp_insert_post()

[kasparsd]

Recent versions of MySQL (v8) and MariaDB server now use utf8mb3_* instead of utf8_* (an alias of utf8mb3) for collations/charsets. This makes WP skip the encoding of emojies when it should happen.

Trac ticket: https://core.trac.wordpress.org/ticket/60362

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[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 61110
GitHub commit: dbab14a

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.