Description:
------------
With Enum, ReflectionMethod->getDeclaringClass() return a ReflectionClass object instead of ReflectionEnum.

The RFC is unclear about that. But ReflectionEnum extends ReflectionClass, so the types are compatible and it's more logical.
We are forced to use the enum_exists() function, and rebuild a new ExceptionEnum if we need ReflectionEnum.

Test script:
---------------
<?php

Enum testEnum {
    case A;
    case B;
    
    public function foo () {}
}

$re = new ReflectionEnum(testEnum::class);
$me = $re->getMethod('foo');

echo $me->getDeclaringClass()::class;

echo "\n";

$rc = new ReflectionClass(testEnum::class);
$mc = $re->getMethod('foo');

echo $mc->getDeclaringClass()::class;

Expected result:
----------------
ReflectionEnum
ReflectionEnum

Actual result:
--------------
ReflectionClass
ReflectionClass