Bug 1605934 - Use nested namespaces r=sg

Done with:
./mach static-analysis check --checks="-*, modernize-concat-nested-namespaces" --fix .
and then clang-format on the files

Differential Revision: https://phabricator.services.mozilla.com/D58217

js/src/frontend/BinASTParserPerTokenizer.cpp

@@ -74,8 +74,7 @@
 //
 // They should be treated lazily (whenever we open a subscope), like bindings.
 
-namespace js {
-namespace frontend {
+namespace js::frontend {
 
 using UsedNamePtr = UsedNameTracker::UsedNameMap::Ptr;
 
@@ -811,5 +810,4 @@ BinASTParserPerTokenizer<Tok>::asFinalParser() const {
 template class BinASTParserPerTokenizer<BinASTTokenReaderContext>;
 template class BinASTParserPerTokenizer<BinASTTokenReaderMultipart>;
 
-}  // namespace frontend
-}  // namespace js
+}  // namespace js::frontend