Rename the Bluetooth profile classes for HID Device role.

We already have BluetoothInputDevice class, so adding something
called BluetoothHidDevice seems confusing. On the other hand,
the new class is designed to connect to HID Host devices, so
naming it BluetoothInputHost makes sense and goes in line with
the existing BluetoothInputDevice.

The same goes for the new constant HID_DEVICE that is just as
confusing to have together with the INPUT_DEVICE one.

This CL also renames the "connection state changed" broadcast
(for the same reasons), declares it as an SDK constant, and also
adds some javadoc to it.

Note that BluetoothHidDeviceApp* classes remained unchanged, as
those correspond to the app that implements the Device (and
connects to the Host).

Test: make
Change-Id: I5075ca5b97db3c1dd403c2e9660eecc7380cffe2