Add `PointerRNA::reset()` and `PointerRNA::invalidate()` utils functions
(both simply reset the PointerRNA data to empty state).
Replace `RNA_POINTER_INVALIDATE` macro by `PointerRNA::invalidate()`.
Follow-up to !134393 and e55d478c64.
Add `PointerRNA::reset()` and `PointerRNA::invalidate()` utils functions
(both simply reset the PointerRNA data to empty state).
Replace `RNA_POINTER_INVALIDATE` macro by `PointerRNA::invalidate()`.
Follow-up to !134393 and e55d478c64.