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>
diff --git a/test/identifiers/underscore/prefix/upper/struct.wgsl.expected.msl b/test/identifiers/underscore/prefix/upper/struct.wgsl.expected.msl
index bafed70..cc20aac 100644
--- a/test/identifiers/underscore/prefix/upper/struct.wgsl.expected.msl
+++ b/test/identifiers/underscore/prefix/upper/struct.wgsl.expected.msl
@@ -4,6 +4,7 @@
 struct A {
   int B;
 };
+
 struct _A {
   int _B;
 };