PHP 8.x: various compatibility fixes for WordPress 6.3

[hellofromTonya]

Previously:

• #56790 (6.2)
• #55656 (6.1)
• #54730 (6.0)
• #53635 (5.9)
• #50913 (5.6)

This ticket will be used as an "epic", allowing a variety of small patches each fixing a specific failure to be added to and committed against this ticket.

For patches addressing all instances of failures related to one specific PHP version (such as PHP 8.0, 8.1, or 8.2) change across the codebase, separate tickets should still be opened.

For an example of issues/patches with separate tickets, see:

• #53299 PHP 8.1: Update is_serialized function to accept Enums
• #53465 PHP 8.1.: the default value of the flags parameter for htmlentities() et all needs to be explicitly set

When opening a separate ticket, please tag it with the appropriate PHP version keyword so that these tickets can be easily found:

• PHP 8.2: keyword is php82 with its report https://core.trac.wordpress.org/query?keywords=~php82
• PHP 8.1: keyword is php81 with its report https://core.trac.wordpress.org/query?keywords=~php81
• PHP 8.0: keyword is php8 with its report https://core.trac.wordpress.org/query?keywords=~php8

[SergeyBiryukov]

Replying to drzraf:

Could you please consider changesets r54349 and/or r54351 which weren't merged but are necessary to avoid the rtrim(): Passing null to parameter #1 ($string) of type string is deprecated

Those changesets were merged in WordPress 6.1 and are still included in 6.2.

The deprecation notice could be triggered by a plugin or theme, does it still happen on a clean install?

Also, looking at comment:133:ticket:54504, might be a good idea to confirm that the site did in fact successfully update to 6.2, e.g. by doing a full file comparison.