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/type_java.cpp b/type_java.cpp
index cb3ab35..bd1b700 100644
--- a/type_java.cpp
+++ b/type_java.cpp
@@ -29,6 +29,7 @@
 
 namespace android {
 namespace aidl {
+namespace java {
 
 Expression* NULL_VALUE;
 Expression* THIS_VALUE;
@@ -1103,5 +1104,6 @@
   }
 }
 
+}  // namespace java
 }  // namespace aidl
 }  // namespace android