Add some SkSL intrinsics to our dm tests.

This CL adds dm coverage for:
- abs(half)
- sign(half)
- floor
- ceil

And creates test output for abs(int) and sign(int); these aren't covered
by dm because they don't exist in ES2 and so are unsupported by Runtime
Effects.

Change-Id: Ia3e660408cef50dec8fa4b6bdc12906e96179f6e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/360419
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
34 files changed