st/wgl: add support for multisample pixel formats
st/wgl: add support for multisample pixel formats

Create pixel formats with 0, 4, 8 and 16 samples per pixel.
Add a SVGA_FORCE_MSAA env var to force creating all pixel formats
with a particular sample count.  This is useful for testing Mesa/GLUT/
etc. programs which don't ordinarily use multisample.

Reviewed-by: Matthew McClure <e6755070b8e938430a7421a62f674981cef08a75@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler