Autogenerating the following code:
- extension enum
- extension-to-string
- string-to-extension
- capability-to-string
Capability mapping table will not compile if incomplete.
TODO: Use "spirv-latest-version.h" instead of 1.1.
Added function to generate capability tables for tests.
Known extensions are saved in validation state. Unknown extension
produce a dignostic message, but do not fail the validation.
Moved extension definitions to their own file.
