GeometryShaderGen: Add an option to render thin lines as line primitives.

[CrossVR]

This is a speed-hack option that introduces graphical inaccuracies if enabled.

Here are two screenshots for comparison:

Speed-hack on: https://www.dropbox.com/s/dtt0lou77fcnzna/00000000-2.png?dl=0
Speed-hack off: https://www.dropbox.com/s/yp2whv5o1d87ao0/00000000-3.png?dl=0

I've also enabled this speed-hack by default for lines that have a width of <=1px in the hopes that it will not affect the FIFO-CI output. It likely will, in which case I'll test ==1px and see if we can get away with that. Couldn't get away with any of that, lines now render as normal when the speed-hack is disabled.

I'm still attempting other solutions for this problem without the need for a speed hack, do not merge this PR.

[fuel-pcbox]

Rogue Squadron 2 HUD icons missing

Ya dun fucked up, m8.

[lioncash]

What's the the rationale for this? I'm reluctant to to agree to merging this if there's no other reason than "It makes it faster and inaccurate at the same time". I'm assuming that's not the case, but that's all I can make of it with the commit message.

[degasus]

This won't work for "thin" lines at a higher resolution. They all will be wide lines :/

For performance, we should try to always have a geometry shader enabled. I doubt it's a GPU slowdown, more likely a driver issue because of enable/disable a shader stage (does this require a GPU pipeline flush?)

[CrossVR]

@degasus The problem is that you get a performance hit as long as the geometry shader stage is active, even if it is a basic passthrough geometry shader.

But it could indeed be true that the enable/disable causes the performance hit to be even greater.

[CrossVR]

Seems like geometry shaders were not responsible for the observed slowdown, closing this pull request.