Interpreter: Disallow recursion

I think this is the minimum rule that's easy to understand when writing
SkSL for the interpreter that ensures we'll be able to statically
determine total stack usage of a particular function.

While writing the new test, I also noticed that we still return
(invalid) byte code, even when there are errors. Fixed that.

Change-Id: I625a8592c9ba1656074e5f0d4227d41968af7b37
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226218
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed