Add Android information service to send API level

Register the Android information service as a custom service when
the Android API level is defined. Send the API level as a characteristic.

Bug: 348512828
Bug: 351860033
Test: m com.android.btservices
Flag: android_os_identifier
Change-Id: Ifcdfa4b8b05d7bf32d4b1a285ea2d5c0d8f7f42c