Expose generic uniform-write ability.

Internally, uniform gathering used a generic method based on the
SkSLType of the uniform, but the exposed methods only allowed writing
(a subset of) those uniform types, via overloads/type deduction.
It's easiest for Runtime Effects to write the uniforms generically,
using the SkSLType approach.

This CL exposes the SkSLType-based approach publicly, and makes it
work properly with the UniformExpectationValidator.

Change-Id: I7484859fba664bd422e270a57d59fd49cb2c54c0
Bug: skia:13457
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/554079
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed