Set default value of accessibility button mode

Set floating menu mode by default, but if the user uses accessibility button in the navigation bar to trigger their accessibility features before migration, then set it to keep the navigation button mode.

Cherry picked from commit a87f05d5

Bug: 173940304
Test: 1. Push old version of db and apk
      2. Enable/Disable accessibility features in navigation bar
      3. Push new version of db and apk
Change-Id: I465eb2190f0e1ca9a6a6be928752a07d5e9576da
Merged-In: I465eb2190f0e1ca9a6a6be928752a07d5e9576da