ReflectionProperty::isInitialized() without arguments diverges from native (returns bool instead of throwing)

[lisachenko]

Pre-existing parity gap documented during the #223 investigation (see PR #228, "Deliberately not fixed" notes; kept out of that PR's scope).

Go\ParserReflection\ReflectionProperty::isInitialized() called with no argument (null) returns hasDefaultValue(), whereas native reflection throws a TypeError for a non-static property when no object is supplied (for static properties native answers about the static value).

Expected: mirror the native contract — TypeError for instance properties with null, real answer for static properties.