Change navbar icons when overview proxy service is enabled (1/2)

Changed the home button to a longer bar oval shape and back button to be
outlined instead of filled. Change opalayout to make the home button
larger when connected to launcher. Decrease the nav icons by 2dp in size.

Bug: 67957962
Test: manual
Change-Id: Ia70ea6704278948e333cb9540ff599dbe657de2c