!UPSTREAM: write out cut bits

Stuff that needs fixing:
- Not yet configuring 3DSTATE_GS to indicate that cut bits are present
- Not handling >31 output vertices correctly
- Don't know if I have an off-by-1 error
- Probably should pack vertex_count and cut_bits into a single register
- Code should be conditioned on whether the shader uses EndPrimitive()
- At end of thread, shouldn't do the write if vertex_count is a multiple of 32
- At end of thread, should write to the appropriate DWORD
- At EmitVertex time, should write cut bits if vertex_counter%32 == 31
!UPSTREAM: Configure cut bits
Experiment: don't write cut bits
Experiment: use data header size of 0
Whoops, should have used offset of 1
Change emit_vertex to add to offset so that GS with many outputs works correctly with cut bits
Revert "Experiment: use data header size of 0"

This reverts commit 2be9126c7a7b869c9f32e113ba66f8b2c1c4f3aa.
Revert "Experiment: don't write cut bits"

This reverts commit 01587694facf8e035f5df2acd0d70874b3cca2bf.
Fixup message len for thread end considering the possibility of EndPrimitive
Fixup EndPrimitive to not use immed in a prohibited position