LRUCache: cache will unload currently used tiles when sharing

[gkjohnson]

If an LRUCache is shared between multiple tile renderers and suddenly only a single tile set is updated then all the tiles will be marked unused and tiles from the non-updated tileset will be removed even though they're visible.

The solution is to explicitly mark and unmark tiles as used and unused in the LRCache per tiles renderer so sibling renderers are not affected.