Create polyfills for str_contains(), str_starts_with() and str_ends_with() for PHP 8

[superpoincare]

PHP 8 will have new functions str_contains(), str_starts_with() and str_ends_with()

These are going to be popular and there are some who aren't developers but can copy/paste from websites. This creates the risk that they might copy paste some code involving these functions while not being upgraded to PHP 8 in their servers.

So it will be useful if these have polyfills in core.

[jorbin]

This request is already being tracked in #49652