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/AutoVersioner.cpp b/tools/aapt2/link/AutoVersioner.cpp
index 11fcc5d..c7e603e 100644
--- a/tools/aapt2/link/AutoVersioner.cpp
+++ b/tools/aapt2/link/AutoVersioner.cpp
@@ -31,7 +31,7 @@
                                      const int sdkVersionToGenerate) {
     assert(sdkVersionToGenerate > config.sdkVersion);
     const auto endIter = entry->values.end();
-    auto iter = std::lower_bound(entry->values.begin(), endIter, config, cmp::lessThan);
+    auto iter = std::lower_bound(entry->values.begin(), endIter, config, cmp::lessThanConfig);
 
     // The source config came from this list, so it should be here.
     assert(iter != entry->values.end());
@@ -124,7 +124,7 @@
                                 auto iter = std::lower_bound(entry->values.begin(),
                                                              entry->values.end(),
                                                              newConfig,
-                                                             cmp::lessThan);
+                                                             cmp::lessThanConfig);
 
                                 entry->values.insert(
                                         iter,