Shader generator: Move FS_TEX_ALPHA to a uniform bool.

[hrydgard]

Part of #16567, the effort to reduce the number of unique shaders/pipelines we generate. This does make a difference and I can't see any performance difference otherwise.

This is the first time we use uniform bools. If needed, can easily switch it to a float. If we were only targeting modern APIs I'd just make a uint bitfield of course.

For some reason, this doesn't work with D3D9 yet. works now!

Had to expand the uniform buffer again, but will optimize it down again later, though I think it doesn't matter too much.

Needs some testing on older OpenGL before merge.

[hrydgard]

Hm, first thought bool registers had some strange behaviors in D3D9, like getting locked at the first use or something. But tried switching to float locally, and it's still just as broken. Hm.

EDIT: Argh, just forgot to add to psUniforms...

No clue why the test errors :( It all works fine at runtime..

[unknownbrackets]

https://social.msdn.microsoft.com/Forums/vstudio/en-US/ff6328b5-a627-422c-956a-67eba9a54b4a/wpf-effect-creation?forum=wpf

Maybe it's something with the emulated D3D 9 running here, maybe it only supports 2.0?

-[Unknown]

[hrydgard]

Ah, likely something like that.

I'm just gonna change it to a float, easier for old bad shader compilers to deal with...