[Android] Fix that R.class in core library is set with incorrect value

The R.java chromium build process for apk generated in the
trival target based on xwalk_core_library is with incorrect
value set.

However, what we needed is the declare class from resource map
instead of the one with value. To fix this, build
xwalk_core_library_empty target as test apk to exclude resource
generation, besided add resource map as additional src to include
the correct declaration of R.java.

Thus, the R.class was missed in xwalk_core_library_java,
caused by https://crosswalk-project.org/jira/browse/XWALK-1575
The gyp keyword 'all_dependency_settings' doesn't work on the
target 'chromium_generated_java' for variable 'jar_final_path' which
normally is declared in 'build/java.gypi'

Currently, explicitly add the jar from chromium_generated_java into
the list.

Rename the empty apk target to xwalk_core_library_empty_embedder_apk,
It's more precise and to avoid incorrectly packaging the legacy
classes in previous target's output folder.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1577