lowpan: Introduce C++ versions of various java classes

This change introduces C++ versions of the following java classes:

 * android.net.lowpan.LowpanIdentity
 * android.net.lowpan.LowpanCredential
 * android.net.lowpan.LowpanProvision
 * android.net.lowpan.LowpanBeaconInfo
 * android.net.lowpan.LowpanChannelInfo

Bug: b/63707448 b/63708348
Test: Confirmed with unit tests from change id
      I41d590b1e77dc41873c4b9e9bf1b7f1bf859f74e

Change-Id: I3dc7b9ca3b33b2ee5f92c8f76c28710997fb931d
12 files changed