Metal 1.x does not support swizzling on packed_vec types.
Use array-index for single element selection (permitted on LHS and RHS of assignment)
Cast the packed_vec to a vec for multiple element swizzles (not permitted as the LHS of an assignment).
Fixed: tint:1249
Change-Id: I70cbb0c22a935b06b3905d24484bdc2edfb95fc2
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/67060
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Ben Clayton