glamor: Add infrastructure for generating shaders on the fly

glamor: Add infrastructure for generating shaders on the fly

This just adds a bunch of support code to construct shaders from
'facets', which bundle attributes needed for each layer of the
rendering system. At this point, that includes only the primitive and
the fill stuff.

v2: Correct comment in glamor transform about 1/2 pixel correction needed
    for GL_POINT. (Eric Anholt)
v3: Rebase on Markus's cleanups (change by anholt)

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>