Fix visibility rules for configs enforced by latest GN.

Prior versions of GN had a bug (gn:22) where visibility rules
for configs weren't enforced properly.

This CL tweaks the visibility settings of some configs to conform
to the latest version.

Change-Id: If0e9f06667d3d89bcd0bbfc938e159e590e11e27
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/26929
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/common/BUILD.gn

@@ -84,8 +84,9 @@ config("dawn_internal") {
   }
 
   # Only internal Dawn targets can use this config, this means only targets in
-  # this BUILD.gn file.
-  visibility = [ ":*" ]
+  # this BUILD.gn file and related subdirs.
+  visibility = [ "../*" ]
+
   cflags = []
 
   # Enable more warnings that were found when using Dawn in other projects