Add $filter parameter for ReflectionClass::(getConstants|getReflectionConstants)

This solves [#79628](https://bugs.php.net/79628).

Similar to `ReflectionClass::getMethods()` and `Re

Add $filter parameter for ReflectionClass::(getConstants|getReflectionConstants)

This solves [#79628](https://bugs.php.net/79628).

Similar to `ReflectionClass::getMethods()` and `ReflectionClass::getProperties()`,
this new `$filter` argument allows the filtering of constants defined in a class by
their visibility.

For that, we create three new constants for `ReflectionClassConstant`:

* `IS_PUBLIC`
* `IS_PROTECTED`
* `IS_PRIVATE`

Closes GH-5649.

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