Correctly manage the lifecycle of IME InputChannels.

InputChannels are normally duplicated when sent to a remote process
over Binder but this does not happen if the recipient is running within
the system server process.  This causes problems for KeyGuard because the
InputMethodManagerService may accidentally dispose the channel
that KeyGuard is using.

Fixed the lifecycle of InputChannels that are managed by the IME
framework.  We now return a duplicate of the channel to the application
and then take care to dispose of the duplicate when necessary.
In particular, InputBindResult disposes its InputChannel automatically
when returned through Binder (using PARCELABLE_WRITE_RETURN_VALUE).

Bug: 8493879
Change-Id: I08ec3d13268c76f3b56706b4523508bcefa3be79