Add Rasterizer state support

[kvark]

Rasterizer state is (in this context) the configuration of fixed-function hardware functions (i.e. fragment shader is not a part of this state) that are responsible for bringing the output geometry to the framebuffer. It can include the following blocks (roughly in the order they are executed by HW):

• Viewport (optionally - leave that to framebuffer to manage in Implement framebuffer binding and Surface creation #50)
• Primitive setup (points/lines/triangles, face culling)
• Polygon offset
• Multisampling
• Scissor
• Stencil (test, mask)
• Depth (test, mask)
• Blending (equation)
• Color mask

We could have them stored in one big descriptor (either passed with every draw call - heavy, immutably defined and represented by a handle), or split into groups:

1. Rasterization (primitive, culling, offset, multisample)
2. Mask (Scissor, stencil mask, depth mask, color mask)
3. Depth-stencil (functions, params)
4. Blending (equation, params)

The reason why I put masks into a separate group with scissor is because it's a subset of the only states that affect Clear function.

[kvark]

For the reference, D3D has the following state groups (listing only relevant ones):

1. Rasterizer
   • Viewport
   • Scissor test
   • Primitive setup
   • Polygon offset
   • Multisampling
2. Output Merger
   • Depth test
   • Stencil test & op
   • Blending
   • Color mask

When I thought about the rasterizer state as a whole, I was imagining what parameters transform feedback (aka stream-out in D3D) will not have comparing to a regular draw call. Apparently, we can't ignore the primitive setup when the rasterizer is off, because primitives are still constructed when the tessellation is ON, and this can be done with transform feedback.

Another thing is the clear operation. OpenGL clear still respects the scissor test as well as write masks for color, depth, and stencil, but nothing else. Perhaps, we can pass only the Scissor block to the clears, and only the Primitive block to transform feedbacks?

For the regular draw calls, both OM and Rasterizer are part of the fixed-function pipeline state. Both can not be derived automatically for the general case, hence to be provided. Is there much sense then to split the whole state into Rasterizer + OM? Instead, we can just have all the state blocks be a part of a larger structure.

[kvark]

Head's up - renaming 'rast' to 'state'

[kvark]

Multisampling is moved to #137, all other missing states are covered by #138.