Adds enemy_struck and self_struck temporal scripts + z_index fix

Adds enemy_struck and self_struck temporal scripts These work as the opposite of enemy_hit and self_hit, triggering when you are struck by an attack, rather than when you hit with an attack

I also changed the wording on enemy_hit and self_hit, because I feel it is less confusing. Not a deal breaker if you hate that and want it reverted.

Also adds fix for bad z_indexing on backdrop, the fix involved just shifting up the z_index of all layers above it by 10.