AAPT2: Fix inclusion of comments in R.java javadoc

Comments weren't being copied when merged from the various
resource tables.

Also refactored the JavaClassGenerator to omit a class
if no entries exist for it.

Change-Id: I6eaa89b7b3715bc05403635a2baf0d1db3efd142
diff --git a/tools/aapt2/link/TableMerger.cpp b/tools/aapt2/link/TableMerger.cpp
index 636c2ba..0bcb5ba 100644
--- a/tools/aapt2/link/TableMerger.cpp
+++ b/tools/aapt2/link/TableMerger.cpp
@@ -122,7 +122,7 @@
 
             for (ResourceConfigValue& srcValue : srcEntry->values) {
                 auto iter = std::lower_bound(dstEntry->values.begin(), dstEntry->values.end(),
-                                             srcValue.config, cmp::lessThan);
+                                             srcValue.config, cmp::lessThanConfig);
 
                 if (iter != dstEntry->values.end() && iter->config == srcValue.config) {
                     const int collisionResult = ResourceTable::resolveValueCollision(