Interpreter: Implement ternary operator

Change-Id: If05661224d4a53e1854180d9b280ebb7a7ac2793
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214191
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed