Extend --writeShaders to output SPIR-V

Changed the python script to operate on all shaders in the directory,
handling SPIR-V appropriately, and collating data across backends.
Made the output CSV, so that it imports into spreadsheets directly
(and handles missing columns cleanly).

Removed all the JSON digest logic - this was overkill at the moment,
and it made it tricky once we were combining information from GL and
Vulkan. Also, the hit count data was probably misleading - it didn't
count hits at the program cache level, just the persistent cache.

Change-Id: If354cde943c96f84e7bcc20a137afefca3b59358
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/207960
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
2 files changed