Optimize InputConnection tracing logic a bit

This CL is a follow up CL to our previous CL [1], which introduced
InputConnection logging as part of IME tracing project.

The goal of this CL is to consolidate RemoteInputConnectionImpl by
separating core business logic from orthogonal concept such as method
tracing, without sacrificing the runtime performance.

With this CL, both code and string resource duplicates will be
actually reduced.  There is no additional object allocation unless the
IME tracing is explicitly enabled.

 [1]: Iabd6af1b858803030848a0ef5e7dd9ecfc562716
      0653b692

Bug: 154348613
Bug: 192412909
Test: Manually verified that the IC tracing is still working
Change-Id: I329129241bdae231844dc3170faf9e8d11f49f08