To sort out the issue, main keyboard and mini keyboard have to share
the pointer trackers.
In order to prepare for that, KeyboardView needs to be refactored as
two separate classes. KeyboardView is responsible for drawing keyboard
visual. And LatinKeyboardBaseView is responsible for handling key
event and mini keyboard as well.
Bug: 4768084
Change-Id: I5643e333b9bdfde0c939a0693cea76bd22f38897
