Description:
------------
ReflectionClass::getReflectionConstant() returns false when constant is not found. This is unexpected because all other methods like getMethod() or getProperty() which have equivalent signatures and fuction throw a ReflectionException.

The return value is also not documented.

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

class Foo {}

$barClassReflection = new ReflectionClass(Foo::class);
var_dump($barClassReflection->getReflectionConstant('XXX'));
```

https://3v4l.org/k09Q8

Expected result:
----------------
Throw exception like the other methods on ReflectionClass to behave consistently and document this behavior.