wlr_damage_ring: Add wlr_damage_ring_contains_xxx functions

• Added wlr_damage_ring_contains_region to check if a pixman region is fully contained within the current damage tracked by the ring.
• Added wlr_damage_ring_contains_box to verify whether a wlr_box is fully contained within the current damage.

These functions help determine whether specific areas are already covered by the damage ring.