[android] Soft keyboard fixes

1. Manually request focus for input fields and show keyboard

This is needed when targetting API 28 which doesn't give focus anymore
automatically like it used to be.

Closes #1505

2. Remember keyboard states across screen rotations

This also upgrades the emoji library and gets rid of the
KeyboardAwareLinearLayout that is still a relict from the time when we
were using Signal's emoji implementation.

3. Move soft keyboard showing/hiding into UiUtils