glsl: Rewrite and fix min/max to saturate optimization.

glsl: Rewrite and fix min/max to saturate optimization.

There were some bugs, and the code was really difficult to follow. We
would optimize

   min(max(x, b), 1.0) into max(sat(x), b)

but not pay attention to the order of min/max and also do

   max(min(x, b), 1.0) into max(sat(x), b)

Corrects four shaders from Champions of Regnum that do

   min(max(x, 1), 10)

and corrects rendering of Mass Effect under VMware Workstation.

Cc: "10.4 10.5" <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89180
Reviewed-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>