Move Java related code into a java namespace

This lets us use names like Type instead of CppType for generated
code specific to C++.  C++ code will similarly go in its own namespace.

Bug: 24472672
Test: Compiles, unittests pass

Change-Id: I10fc8ce6436e297eb36c7b63e0c6d78a45bf2a19
diff --git a/aidl.cpp b/aidl.cpp
index 96e81b6..a55724a 100644
--- a/aidl.cpp
+++ b/aidl.cpp
@@ -626,7 +626,7 @@
 int compile_aidl_to_cpp(const CppOptions& options) {
   interface_type* interface = nullptr;
   import_info* imports = nullptr;
-  unique_ptr<JavaTypeNamespace> types(new JavaTypeNamespace());
+  unique_ptr<java::JavaTypeNamespace> types(new java::JavaTypeNamespace());
   int err = load_and_validate_aidl(std::vector<std::string>{},
                                    options.ImportPaths(),
                                    options.InputFileName(),
@@ -645,7 +645,7 @@
 int compile_aidl_to_java(const JavaOptions& options) {
   interface_type* interface = nullptr;
   import_info* imports = nullptr;
-  unique_ptr<JavaTypeNamespace> types(new JavaTypeNamespace());
+  unique_ptr<java::JavaTypeNamespace> types(new java::JavaTypeNamespace());
   int err = load_and_validate_aidl(options.preprocessed_files_,
                                    options.import_paths_,
                                    options.input_file_name_,