Make IInputMethodManager to oneway (4/N)

After CL[1], the client might be waiting forever when
system server throw Exception. The expected behavior
after throwing an Exception from the system server
should let the caller crash.

To keep the previous behavior, support exception as a
valid result for ResultCallback.

CL[1]: If4b40244a2e0e3b11c38c1da9340ba8e5166ad64

Bug: 174263942
Bug: 163453493
Test: Throw an exception in system server and observe the
      caller crash with ResultCallback flow.
Test: atest CtsInputMethodTestCases
Change-Id: If79e063641a01b325c63eb9f871f5b992d7c0b72