Migrate several GLSL workaround unit tests to golden files.

We now support building an SkSL golden output twice, once honoring the
custom #pragma settings, and once more ignoring the settings. This
allows us to see the output of the workaround technique, alongside the
"default-settings" output which should not contain a workaround.

To implement this, skslc now supports a flag: --[no]settings.
When it's set, /*#pragma settings*/ comments are honored. When it's not
set, skslc ignores the comments. compile_sksl_tests.py passes this flag
along to skslc.

This approach is not strictly limited to workarounds; the
"TypePrecision" GLSL test was also updated to use this technique.

Change-Id: I79204df047b024533ed6bc1f4c088e0e878d5bb1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317246
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
30 files changed