[PhpUnitBridge] Add enum_exists mock

Author: alexandre-daubois

components/phpunit_bridge.rst

@@ -736,6 +736,7 @@ reason, this component also provides mocks for these PHP functions:
 * :phpfunction:`class_exists`
 * :phpfunction:`interface_exists`
 * :phpfunction:`trait_exists`
+* :phpfunction:`enum_exists` (requires PHP 8.1)
 
 Use Case
 ~~~~~~~~
@@ -798,6 +799,13 @@ classes, interfaces and/or traits for the code to run::
         }
     }
 
+Note that mocking a class with ``ClassExistsMock::withMockedClasses()``
+will make :phpfunction:`class_exists`, :phpfunction:`interface_exists`
+and :phpfunction:`trait_exists` return true.
+
+To register an enumeration and mock :phpfunction:`enum_exists`,
+``ClassExistsMock::withMockedEnums()`` must be used.
+
 Troubleshooting
 ---------------