restrict was supported, but it broke in MSL 3.0. __restrict works on all
versions, so opt for that instead.
Also check for RestrictPointer decoration and refactor to_restrict() to
not take optional parameter to make it more obvious when implied space
character is added.
- Determine sizing and alignments of pointers to types as
distinct from the size and alignment of the types themselves.
- Declare all buffer pointers in the MSL device address space.
- Support struct pointer recursion, where structs can
contain pointers to themselves or to a parent struct.
- Add SPIRType::was_forward_referenced to track if a type was forward
referenced, to help emit MSL structs in the correct dependency order.
- Handle pointers to pointers that are not just arrays of arrays.
