Mesh shader emulation over draw-indirect

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Based on #33

Initial implementation is practically working, this ticket is to track technical depth and for profiling work.

TODO:

• Lines/Points
• test flat and other interpolators
• Fix in uvec3 gl_WorkGroupIDpolution
• Fix in uvec3 gl_NumWorkGroups - polluted due to dispatch indirect
• Fix in uvec3 gl_GlobalInvocationID // polluted, since it is byproduct of gl_WorkGroupID
• Control/sanitize out-of-memory case
• perprimitiveEXT - no immediate need

ERR(wont't fix):

• Draw order is lost inside a single draw-call (not an issue for 3D)

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Profiler view on NV (native mesh-shader is disabled):

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New idea on how to avoid scratch buffer traffic problems(and make solution more Intel-friendly): Decouple .mesh into separate index and vertex shaders. This can be done, for the most cases, if vertex computation is uniform-function.

uniform-function to me is: Function that can use only constants, locals, uniforms, read-only ssbo, push-constants in various combinations and have no side-effects. Similar to pure function in a way, but less restricted. This will allow to move most of computation to vertex shader.

The only problem is gl_WorkGroupID.x that is used all over the place

Update to strategy:

Cross-thread semantics is a big issue.
different thread can populate different parts of gl_Positions/varying.

Initial toughs: for any write-out store
out[exp1] = exp2;
analyze exp1, exp2:
exp2, like been said: constant-uniform-input expression
exp1 - simple function of gl_LocalInvocationID
all other parts of left side (.x) - straight constants

for all possible values of gl_LocalInvocationID [0..31), engine should populate mapping table, for each varying:
gl_LocalInvocationID <--> id in var[id]

if all varyings are written from same thread, than that gl_LocalInvocationID can be written out to index-buffer

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Initial work on ShaderAnalyzer in 203ab2d.

Can roughly estimate thread-mapping for vertex/varyings for simple(OpenGothic) cases.
TODO: handle more advance control flow instructions.

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Mesh-emulation still slower than draw-call spam in opengothic case.
Hi-Z pass become surprisingly expensive: ~1.4ms in NVIDIA, with total 162k triangles.

Current ideas:

1. Render only closemost pieces if HiZ (possible false holes)
2. Cull HiZ against itself
   a. Draw close-most normally, cull others against previous HiZ
   b. Since HiZ is 64x64 at most, compute-driven rasterization is possible

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Testing FPS on Intel UHD:

	SM	NoSM
DrawIndexed	38	53
Compute	24	32
Compute+Vertex	29	40

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More numbers:

		HiZ(M)	HiZ(sort)	HiZ(draw)	HiZ	SM0	SM1	BasePass	Transparent	FPS
Nvidia	native(MS)				0.14					222
Intel	native(DI)									30.05
Nvidia	MS0	0.46	0.53	0.10	1.66	0.36	1.21	5.13	0.8	75.00		«Cake» shading
Intel										14.2
Nvidia	MS-VS	0.21	0.17	0.67	1.05	0.24	0.47	1.23	0.09	86		VRAM, L1 pressure in draw
Intel										19.2