Add functionality to fix-storage-class so that it can fix up mismatched
data types for pointers as well.
Fixes bugs in when fixing up storage class.
Move GenerateCopy to the Pass class to be reused.
The spirv-opt change for #2535.
This pass tries to fix validation error due to a mismatch of storage classes
in instructions. There is no guarantee that all such error will be fixed,
and it is possible that in fixing these errors, it could lead to other
errors.
Fixes#2430.
