tint: Standardize the way we forward-declare

Style guide has been updated to describe the style in use.

Change-Id: I3fc08e3440566106582695f4dc149fa67d8b8dc8
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86303
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/tint/transform/array_length_from_uniform.h

@@ -24,7 +24,7 @@
 // Forward declarations
 namespace tint {
 class CloneContext;
-}
+}  // namespace tint
 
 namespace tint::transform {
 

src/tint/transform/calculate_array_length.h

@@ -23,7 +23,7 @@
 // Forward declarations
 namespace tint {
 class CloneContext;
-}
+}  // namespace tint
 
 namespace tint::transform {
 

src/tint/transform/decompose_memory_access.h

@@ -23,7 +23,7 @@
 // Forward declarations
 namespace tint {
 class CloneContext;
-}
+}  // namespace tint
 
 namespace tint::transform {
 

src/tint/transform/glsl.h

@@ -22,7 +22,7 @@
 // Forward declarations
 namespace tint {
 class CloneContext;
-}
+}  // namespace tint
 
 namespace tint::transform {
 

src/tint/transform/num_workgroups_from_uniform.h

@@ -21,7 +21,7 @@
 // Forward declarations
 namespace tint {
 class CloneContext;
-}
+}  // namespace tint
 
 namespace tint::transform {