Fix texture scroll, optimise texture matrix operations a bit

[VReaperV]

Fixes #1278.

The previous code assumed that a texture with a scroll textureMod would always wrap around when scroll * backEnd.refdef.floatTime == floor( scroll * backEnd.refdef.floatTime ). This is incorrect if the texture matrix had already been modified by another texMod, so the relevant values are no longer 1.0f and 0.0f. Fix this by using scrollPeriod[0] / ( matrix[0] + matrix[4] ) and scrollPeriod[0] / ( matrix[0] + matrix[4] ) to get the actual time at which wrap-around for x and y will occur, and use fmodf( backEnd.refdef.floatTime, period ) to get the part that is equivalent to just using backEnd.refdef.floatTime, but without the value getting continuously larger.

Also NUKED some useless matrix computations from texMod scroll, and added some functions to only calculate the relevant part of a matrix for texture matrices.

This change can be observed on:
Map tds, r_forceRendererTime 49999 and r_forceRendererTime 50000:
Old:
https://imgsli.com/MzQ0MjYy
New:
https://imgsli.com/MzQ0MjY1
Map pulse, r_forceRendererTime 50000 and r_forceRendererTime 50001:
Old:
https://imgsli.com/MzQ0MjY0
New:
https://imgsli.com/MzQ0MjY2

[slipher]

At another spot on Pulse, with this PR I get a new instance of the scrolling glitch where there wasn't one before. The lorem ipsum star wars text thing at the spectator spawn only shows the first 2 lines then resets.

[VReaperV]

Oh, right, there were some divs by 0 and a wrong index. Fixed now.

[slipher]

I tried combining a rotate with a scroll and it still suffers from discontinuity:

textures/pulse/title
{
	qer_editorimage textures/pulse/title.jpg

	noPicMip

	surfaceparm noimpact
	surfaceparm nolightmap
   	surfaceparm trans
	surfaceparm nomarks
	{
		map textures/pulse/title.jpg
		tcMod rotate 5
		tcMod scroll 0 0.025
		blendFunc add
	}
}

This could still be merged as-is though, as it fixes some things and doesn't break anything that is not already broken AFAIK.

[slipher]

These probably don't need to be in q_shared.h which is included by all files.

[VReaperV]

Yeah, I guess I can move those to tr_shade_calc.cpp. I had just put those near where the original declarations were, no other reason.

[VReaperV]

I've moved these to tr_shade_calc.cpp now.

[VReaperV]

I tried combining a rotate with a scroll and it still suffers from discontinuity:

textures/pulse/title
{
	qer_editorimage textures/pulse/title.jpg

	noPicMip

	surfaceparm noimpact
	surfaceparm nolightmap
   	surfaceparm trans
	surfaceparm nomarks
	{
		map textures/pulse/title.jpg
		tcMod rotate 5
		tcMod scroll 0 0.025
		blendFunc add
	}
}

This could still be merged as-is though, as it fixes some things and doesn't break anything that is not already broken AFAIK.

Fixed, also fixed some more potential divisions by 0.

[slipher]

The rotation+scroll shader I wrote above got more buggy with the latest code. It still makes discontinuous jumps, and also seems to accelerate faster and faster over time.

[VReaperV]

Hmm, I probably messed something up before pushing to the remote.