This commit adds an app that will be served as BinderTransport example
later.
Currently the app simply calls C++ function when button is pressed. In
the future the C++ function will run BinderTransport gRPC example
instead.
Tests not included in this commit, later we will add a build test to
CI to make sure this apk is always build-able. (This app will also be
used to make sure our BinderTransport implementation is compile-able
with Android toolchain, on GitHub) For now we exclude this target in
bazel build test.
Changes are made to WORKSPACE file in order to support android builds.
Build instructions are documented at
examples/android/binder/java/io/grpc/binder/cpp/example/README.md