Migrate dedicated SPIR-V tests to golden outputs.

There were a surprisingly small number of dedicated SPIR-V tests.
SkSLSPIRVBadOffset was the only test that didn't already exist in the
golden outputs, although it actually contained two tests.

The SPIRVTest.cpp file has been converted to SPIRVTestbed.cpp, which can
be used for local debugging of SPIR-V issues via dm (like GLSLTestbed
and MetalTestbed).

Change-Id: I978d8a7cf5735af7f537113d2b9411ce42cfcf88
Bug: skia:10694
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/338756
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
8 files changed