Add abs support to RP codegen.

This causes four additional tests to pass:
38/113: PASS intrinsics/MinUint.sksl
41/116: PASS intrinsics/MaxUint.sksl
47/133: PASS intrinsics/AbsInt.sksl
48/134: PASS intrinsics/AbsFloat.sksl

Change-Id: I7870b6f78a48141e9b9229a313c5038d988b6e28
Bug: skia:13676
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/626276
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed