Implement distance intrinsic in RP codegen.

This is implemented in terms of the existing `length` intrinsic.

Change-Id: Ib2cfc0e5078e10e571551a9ee37f7911b62e2e66
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/657738
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed