Introduce new PHP cross-version compatibility functions, `str_contains()`

[knutsp]

PHP 8.0 will introduce a new function, str_contains(). The function return true or false depending on the second parameter, string $needle, is found in the first parameter, string $haystack. The RFC can be found here ​https://wiki.php.net/rfc/str_contains

if ( ! function_exists( 'str_contains' ) ) {
    function str_contains( string $haystack, string $needle ): bool {
        return false !== strpos( $haystack, $needle );
    }
}

Including a polyfill now will allow developers to take advantage of the new function and write consistent code regardless of a site's PHP version.

Related: #45055

[ayeshrajans]

Here is a patch to polyfill. We can replace instances with strpos() !== false instances in core if we have this core.

[jorbin]

#51560 was marked as a duplicate.

[hellofromTonya]

Reassigning this ticket and other PHP polyfill tickets to me to get them into 5.9 release.

Trac ticket: https://core.trac.wordpress.org/ticket/49652

[hellofromTonya]

PR 18180 is thoroughly reviewed and ready for commit.

[hellofromTonya]

In 52039:

General: Introduce polyfill for str_contains() added in PHP 8.0.

PHP 8.0 introduced a new function: str_contains(). It performs a case-sensitive check indicating if given substring (needle) is contained in the string to search in (haystack).

This polyfill makes this function available for use in Core.

Ref:

• PHP RFC ​https://wiki.php.net/rfc/str_contains
• PHP manual ​https://www.php.net/manual/en/function.str-contains.php

Props ayeshrajans, costdev, desrosj, hellofromTonya, knutsp, pbearne.
Fixes #49652.

Committed via changeset https://core.trac.wordpress.org/changeset/52039.

[hellofromTonya]

Thank you everyone for your contributions! str_contains() is now available for use in Core.