Add new unit tests for SkSL.

These cover:
- Properly configured out-params
- Invalid/non-lvalue out-params, which currently cause an SkSL crash
- Interactions between the inliner and variable swizzles

Change-Id: I4874101236084f273e704d8717149b431d813883
Bug: skia:10753
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319036
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
7 files changed