Move all Source constructor params to be the first

This consistency can be utilized by the ast::Builder to inject the source parameter if it isn't provided.

Bug: tint:396
Bug: tint:390
Change-Id: I2f19002131e79daae799b8cbe918eb192d6bfc75
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35503
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
diff --git a/src/ast/builtin_decoration.h b/src/ast/builtin_decoration.h
index c907f69..5a1419b 100644
--- a/src/ast/builtin_decoration.h
+++ b/src/ast/builtin_decoration.h
@@ -26,9 +26,9 @@
     : public Castable<BuiltinDecoration, VariableDecoration> {
  public:
   /// constructor
-  /// @param builtin the builtin value
   /// @param source the source of this decoration
-  BuiltinDecoration(Builtin builtin, const Source& source);
+  /// @param builtin the builtin value
+  BuiltinDecoration(const Source& source, Builtin builtin);
   ~BuiltinDecoration() override;
 
   /// @returns the builtin value