iris: Rework iris_update_draw_parameters to be more efficient

iris: Rework iris_update_draw_parameters to be more efficient

This improves a couple of things:

1. We now only update anything if the shader actually cares.

   Previously, is_indexed_draw was causing us to flag dirty vertex
   buffers, elements, and SGVs every time the shader switched between
   indexed and non-indexed draws.  This is a very common situation,
   but we only need that information if the shader uses gl_BaseVertex.

   We were also flagging things when switching between indirect/direct
   draws as well, and now we only bother if it matters.

2. We upload new draw parameters only when necessary.

   When we detect that the draw parameters have changed, we upload a
   new copy, and use that.  Previously we were uploading it every time
   the vertex buffers were dirty (for possibly unrelated reasons) and
   the shader needed that info.  Tying these together also makes the
   code a bit easier to follow.

In Civilization VI's benchmark, this code was flagging dirty state
many times per frame (49 average, 16 median, 614 maximum).  Now it
occurs exactly once for the entire run.