This fixes some cases where entries could have been removed multiple
times reading freed memory. To address this issue this commit removes
duplicates from entries marked for removal and sorts out the removal
process to fix another use-after-free situation.
Another issue fixed in this commit is orphan invalidation cache entries.
Previously only the entries that were invalidated in the current
operations had its entries removed. This led to more use-after-free
situations when these entries were actually invalidated but referenced
an object that didn't exist.
Implement a generic shader cache for fast lookups and invalidations.
Invalidations are cheap but expensive when a shader is invalidated.
Use two mutexes instead of one to avoid locking invalidations for
lookups and vice versa. When a shader has to be removed, lookups are
locked as expected.
