PLS draw shader optimizations

* Don't unpack the color if we're just rendering a clip.

* Pack the gradient data in a way that is faster for the fragment shader to unpack.

Rope: 525-596 fps
187 martys: 106 - 114 fps

Diffs=
7f3990675 PLS draw shader optimizations (#5627)

Co-authored-by: Chris Dalton <99840794+csmartdalton@users.noreply.github.com>