[DocsUI M3] Update styles for the filter bar

1. change the focus ring color to use colorSecondary
2. bring the variable search_chip_radius back to not break the
   overlayable
3. put the padding of the chip group on the group level instead
   of the container level, so it won't show additional space
   when the group is hidden (in Saver mode)

Bug: 382381929
Test: Manually inspect after deployment
Flag: com.android.documentsui.flags.use_material3
Change-Id: I517c0a3e615da91dafe7735a9aca1f767572946b