[Micro-optimizations] Minor Chunk rendering + shader optimizations

[thr3343]

Mix of assorted optimization patches that were too small a justify a PR on their own

Had these patches lying around for a long while now, so decided to combine them together into one PR instead

Will likely not provide more than a +10% FPS improvement at most, however these optimizations have the key advantage of having no effect on visuals, making them effectively free

[deprale]

LGTM :) Thanks for your efforts.

[thr3343]

Parts of this PR are redundant, as some of these optimizations have been added to upstream in a different form
(Namely 6c4fe7d, which has the same benefit as Optimize Entity lighting),
There's also a few minor visual artifacts (i.e. bugs) I failed to notice during testing (Spider shader is visually incorrect)

Also has alot of merge conflicts upstream, so will close and reopen at a later time (likely in a few days)