Add transform/PadArrayElements

Replaces arrays with an explicit stride with an array to a structure holding the element padded with a `[[size]]` decoration.

Note that the HLSL writer is still not correctly emitting structure fields with a `[[size]]`, which will be fixed in a follow up change.

Bug: tint:182
Bug: tint:895
Fixed: tint:180
Fixed: tint:649
Change-Id: Ic135dfc89309ac805507e9f39392577c7f82d154
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54582
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>
Reviewed-by: James Price <jrprice@google.com>

src/resolver/resolver.cc

@@ -2922,7 +2922,7 @@ sem::Array* Resolver::Array(const ast::Array* arr) {
   // records an element count of 0 for it.
   auto size = std::max<uint32_t>(arr->size(), 1) * stride;
   auto* sem = builder_->create<sem::Array>(el_ty, arr->size(), el_align, size,
-                                           stride, stride == implicit_stride);
+                                           stride, implicit_stride);
 
   if (!ValidateArray(sem, source)) {
     return nullptr;