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/struct/type_constructor.wgsl.expected.msl

@@ -7,21 +7,26 @@ struct S1 {
   int c;
   int d;
 };
+
 struct S2 {
   int e;
   S1 f;
 };
+
 struct S3 {
   int g;
   S1 h;
   S2 i;
 };
+
 struct tint_array_wrapper {
   int arr[2];
 };
+
 struct T {
   tint_array_wrapper a;
 };
+
 struct tint_array_wrapper_1 {
   T arr[2];
 };