Changeset 55703

Code Modernization: Replace usage of strpos() with str_starts_with().

str_starts_with() was introduced in PHP 8.0 to perform a case-sensitive check indicating if the string to search in (haystack) begins with the given substring (needle).

WordPress core includes a polyfill for str_starts_with() on PHP < 8.0 as of WordPress 5.9.

This commit replaces 0 === strpos( ... ) with str_starts_with() in core files, making the code more readable and consistent, as well as improving performance.

While strpos() is slightly faster than the polyfill on PHP < 8.0, str_starts_with() is noticeably faster on PHP 8.0+, as it is optimized to avoid unnecessarily searching along the whole haystack if it does not find the needle.

Follow-up to [52039], [52040], [52326].

Props spacedmonkey, costdev, sabernhardt, mukesh27, desrosj, jorbin, TobiasBg, ayeshrajans, lgadzhev, SergeyBiryukov.
Fixes #58012.