AAPT2: Clean up R JavaDoc generation

- Don't generate private attributes in public R.java
- Strip out @SystemApi from comment when generating @android.annotation.SystemApi
- Only emit a single line (up to the first period) of an attribute's comment within
  a styleable's attribute table.

Change-Id: Id6316a6861540325934133958939a12074ad4428
diff --git a/tools/aapt2/java/ClassDefinition.h b/tools/aapt2/java/ClassDefinition.h
index 53e0f6f..d45328f 100644
--- a/tools/aapt2/java/ClassDefinition.h
+++ b/tools/aapt2/java/ClassDefinition.h
@@ -125,7 +125,7 @@
     void writeToStream(const StringPiece& prefix, bool final, std::ostream* out) const override {
         ClassMember::writeToStream(prefix, final, out);
 
-        *out << "public static final int[] " << mName << "={";
+        *out << prefix << "public static final int[] " << mName << "={";
 
         const auto begin = mElements.begin();
         const auto end = mElements.end();