Convert IRGenerator::convertTernaryExpr to TernaryExpr::Make.

Change-Id: I3a9e8b278709485de51dca18b19f6fc7768dde51
Bug: skia:11342
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377098
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
8 files changed