[PM] Update the UI of PIA V2

- If we set the title to be null, it is still the original string in
  Talkback. Change it to an empty string.
- Sent the center vertical of the checkbox in the keepdata layout
- Set not focusable to the button panel to avoid the button panel
  being focused.

Flag: android.content.pm.use_pia_v2
Test: manual
Bug: 274120822
Change-Id: I09c5e928e974289ae436089f16659716edbe0169