Note: This required adding a new test mode to see the AST for vulkan tests.
This also required reworking some deeper parts of type creation, regarding
when storage qualification and constness is deduced bottom-up or dictated
top-down.
There will be subsequent commits to refine semantics, esp. version-specific semantics,
as well as I/O functionality and restrictions.
Note: I'm getting white-space differences in the preprocessor test results,
which I'm not checking in. I think they need to be tagged as binary or something.