General: compatibility with PHP 8.3

[jeherve]

The Core WordPress team is still working on PHP 8.3 compatibility here. While there are still things to change in Core to ensure full compatibility, we can also work on compatibility within the Jetpack plugins.

For a better view of WordPress's PHP compatibility and support, you can refer to this page.

• ci: Test against PHP 8.3 #34312
• codesniffer: Add Jetpack-Compat-83 ruleset #34346
• cli: Fix php version check #36392
• Autoloader: deprecation notice when using PHP 8.3 #37172

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For reference: PHP 8.2 compatibility was tracked in #27927