add an optional, less-accurate-but-faster sprite render and fix silly math bug

[water111]

It's off by default, but you can pick it (sprite-3) with:

It does a few tricks to be faster:

• It reorders all sprite draws to be per-draw mode. This cuts the draw count down a lot. For example, in village 2 near the waterfall there's a spot where you can get around 270 draws with the old and this does 7. It improves frame time from about 7.3 ms to 4.0 ms. (This is a particularly good example, and most of the time the difference is smaller.)
• It uses an index buffer and draws triangle strips. This reduces the number of uploaded vertices, and copying of them from buckets to buffers (you only have to copy indices from the buckets, not entire vertices).
• It uses a more accurate blending mode (the "double draw") for HUD, so the green eco HUD looks right.

But has some disadvantages:

• It doesn't have the fancy multiple-texture trick. If we did this right, we could probably reduce the draw count even more.
• It sorts the sprite draws by their draw mode "key". The developers didn't really have control over sprite draw order, so they got a random order. In some cases, having a non-random ordering looks a bit different (see the waterfall). But, in my opinion, if your computer wasn't fast enough to run the normal sprite renderer, you'd be happier with the slightly wrong sprites than running at <60 fps.

[coveralls]

Pull Request Test Coverage Report for Build 1731688309

• 63 of 509 (12.38%) changed or added relevant lines in 22 files are covered.
• 8 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.2%) to 50.116%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
game/graphics/opengl_renderer/Shader.cpp	0	1	0.0%
game/graphics/opengl_renderer/Sprite3.h	0	1	0.0%
game/graphics/opengl_renderer/tfrag/Tfrag3.cpp	0	1	0.0%
game/kernel/kscheme.cpp	0	1	0.0%
game/runtime.cpp	1	2	50.0%
goalc/compiler/Env.cpp	15	16	93.75%
common/type_system/TypeSystem.cpp	0	2	0.0%
common/type_system/deftype.cpp	4	6	66.67%
game/graphics/opengl_renderer/tfrag/Tie3.cpp	0	2	0.0%
game/kernel/klink.cpp	7	9	77.78%

Files with Coverage Reduction	New Missed Lines	%
common/dma/gs.h	1	0%
game/graphics/opengl_renderer/BucketRenderer.cpp	1	0%
game/graphics/opengl_renderer/Shader.cpp	1	0%
game/graphics/opengl_renderer/tfrag/tfrag_common.cpp	2	0%
goalc/listener/Listener.cpp	3	84.23%

Totals
Change from base Build 1721793615:	-0.2%
Covered Lines:	41149
Relevant Lines:	82108

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💛 - Coveralls