writers: Use the new sem::Module::DependencyOrderedDeclarations

As the resolver currently enforces in-order declarations, this does not
change the declaration order from iterating over the
ast::Module::GlobalDeclarations.

The MSL backend has been changed to use the
sem::Module::DependencyOrderedDeclarations list instead of looping over
different declaration types separately.

Bug: tint:1266
Change-Id: I698d612032285311017bfceab3c42adae1928a0e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/79767
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/expressions/zero_init/struct/array.wgsl.expected.msl

@@ -4,6 +4,7 @@ using namespace metal;
 struct tint_array_wrapper {
   float arr[4];
 };
+
 struct S {
   tint_array_wrapper a;
 };