Simplify FINISH_INPUT_NO_FALLBACK_CONNECTION handling

This is the 6th CL for Bug 26851566 [1][2][3][4][5].

In the CLs [3][5], the approach we took was to extend an existing IPC
method

  IInputMethodClient#setActive(boolean active, boolean fullscreen)

by adding one more parameter "reportToImeController".

However, it seems that such an approach made its handling code hard to
maintain, because the IPC method needed to behave in a completely
different manner depending on the newly introduced parameter.

To avoid such a confusion and to make subsequent refactoring easier,
this CL introduces a new IPC method

  IInputMethodClient#setInteractive(
          boolean interactive, boolean fullscreen)

to clarify what we are actually doing.

In most cases there must be no observable behavior change.  One
possible behavior change is when setInteractive() gets called when
IMM#mCurRootView.getView() is not available.  In the previous CL, we
fell back to previous behavior as if
FINISH_INPUT_NO_FALLBACK_CONNECTION was not defined.  However it looks
like such a fallback mechanism is not an intentional behavior.

The main use case is still verified with existing CTS tests [6][7].

 [1]: Ic11956fe745a829da1ec7c09ea214e9b3961c8e0
      0df88124
 [2]: If06daf71160aa44a4254ac125561974ecbdef4f2
      2c6e80be
 [3]: I8a657e75e274d842fb46b60375f6aeafeab96a59
      152eacec
 [4]: I16f4a34360a2f64b69978724648a9be741f140b5
      3d62f739
 [5]: Id4e71a822bfde5fe6a263bbe094c0d238017efe1
      3d62f739
 [6]: Iba0332ed3b767a9a15768b64947b9cde31105af1
      e2f4138156c784746becde6a01c19f0c3de6ac32
 [7]: I346ef42f2546a2925bf44ca7719ae19399e15e78
      84c5ec2f81d4be5285b9c5f1d0e943f808e9158c

Bug: 26851566
Bug: 156215187
Test: atest InputMethodStartInputLifecycleTest
Change-Id: I0c95d7e70357ac98b336cd1b51a7405ba92a9a6f