ir_to_mesa: Move the STATE_VAR elements of a builtin uniform to a temp (v2).

ir_to_mesa: Move the STATE_VAR elements of a builtin uniform to a temp (v2).

Like the constant handling and the handling of other uniforms, we add
the whole thing to the Parameters, avoiding messy, incomplete logic
for adding just the elements of a builting uniform that get used.
This means that a driver that relies only on ParameterValues[] for its
parameters will have an increased parameter load, but drivers
generally don't do that (since they have other params they need to
handle, too).

Fixes glsl-fs-statevar-call (testcase for Ember).  Bug #29687.

v2: Continue referencing the STATE_VAR[] file directly when the
uniform will land in STATE_VAR[] formatted exactly as we'd put into a
temporary.  When there's array dereferencing, we don't copy-propagate
in Mesa IR (not knowing where the array is in register space), so
smarts here are required or we'll massively increase the temp count.