Remove double support from SkSL.

Doubles are not supported by Metal or GLSL pre-4.0, are not supported in
most backends, and aren't used in any GMs. There isn't any good way to
use them in new code as it would just degrade to float on many of our
supported platforms. (This is assuming that our backends actually know
how to degrade doubles to floats, which is not universally the case.)

Change-Id: Ieacc69db4bdacca104a15a6eef33e05f977d1ffa
Bug: skia:10299
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292846
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
10 files changed