Pass unique_ptr of InputChannel to Connection

This gets us closer to the goal of storing unique_ptr of InputChannel
inside the InputPublisher.

In this CL, we are still allowing the "copy" and "dup" functions to
exist. Removing those requires significant refactoring on the Java side,
including the jni layer and object ownership models.

Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Bug: 161009324
Change-Id: If6f44d78c7fc9f3e12729068de1753847abf0ebb