`str_starts_with()` and `str_ends_with()` were introduced in PHP 8.0 to perform a case-sensitive check indicating if the string to search in (haystack) begins or ends with the given substring (needle).
WordPress core includes a polyfill for these functions on PHP < 8.0 as of WordPress 5.9.
This commit uses `str_starts_with()` and `str_ends_with()` in core files where appropriate:
* `$needle === substr( $string, 0, $length )`, where `$length` is the length of `$needle`, is replaced with `str_starts_with( $haystack, $needle )`.
* `$needle === substr( $string, $offset )`, where `$offset` is negative and the absolute value of `$offset` is the length of `$needle`, is replaced with `str_ends_with( $haystack, $needle )`.
This aims to make the code more readable and consistent, as well as better aligned with modern development practices.
Follow-up to [52039], [52040], [52326], [55703], [55710], [55987], [55988].
Props Soean, spacedmonkey, Clorith, ocean90, azaozz, sabernhardt, SergeyBiryukov.
Fixes#58220.
Built from https://develop.svn.wordpress.org/trunk@55990
git-svn-id: http://core.svn.wordpress.org/trunk@55502 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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