Add unit test for self-referential initializer expressions.

These don't compile in GLSL, so they shouldn't compile in SkSL either--
and fortunately, they do not.

(In C++, and consequently in Metal, these expressions are considered
legal by the grammar and do compile, but generate garbage output.)

Change-Id: I6c7bea70b3d91677ccd8fcbad1eba123d655e856
Bug: skia:10694
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329359
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
3 files changed