Use new PHP 8 function str_contains instead

Problem/Motivation

Use new PHP 8 function str_contains instead. More readable, less instructions, and more efficient.

Steps to reproduce

Proposed resolution

Some examples,

In lib/Drupal/Core/Entity/Plugin/EntityReferenceSelection/PhpSelection.php:122:        
- return strpos($label, $match) !== FALSE;
+ return str_contains($label, $match);

In lib/Drupal/Core/Routing/RouteCompiler.php:101:
-      if (strpos($part, '{') === FALSE) {
+      if (!str_contains($part, '{')) {

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet