Introduce integer vertex attributes

[pchote]

With GL 2.1 out of the picture, we are finally able to use integers and bitwise operations in shaders. This PR replaces the legacy workaround simulating a bitfield with a float to a real bitfield. This allows us to use the full 32 bits of storage, which I use to pack the palette row (as a 16 bit int) to shave 4 bytes off the vertex size.

I expect this should give a minor performance boost, but the focus is on shader readability and maintability.

[pchote]

A future PR could make additional, more invasive, optimisations to reduce the vertex size further: Replace the two (float x, float y) texture coordinates with a single (uint xy) coordinate (saves 8 bytes). The color renderer could then use the first integer to encode the colour (it currently needs all 4 floats), which would allow mods that don't need the second sprite channel to save an additional 4 bytes.

[pchote]

Added some additional improvements.

[PunkPun]

this PR is running ra shellmap at 3FPS, where as on bleed I'm getting 200+

[pchote]

RA shellmap is ~340 FPS for me, compared to ~340 FPS on bleed. Can you have a poke around and try to identify what is causing your perf regression?

[PunkPun]

It seems to be caused by the first commit

within the render loop

[dnqbob]

@PunkPun

Windowed or full screen?

[pchote]

@PunkPun can you please try again on the updated version?

[PunkPun]

LGTM, this is a massive performance and shader readability improvement

[PunkPun]

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