RCFilters: Unify 'highlight' and 'selected' items

RCFilters: Unify 'highlight' and 'selected' items

When moving with the arrows, we don't want a distinction between
the 'selected' and 'highlighted' states, since those don't quite
make sense in RCFilters system. We unify those by always using
'selected' state; this also means that when searching AND when
opening the popup, the first item is 'selected' so the user can
hit 'enter' and add it in, or hit the up/down arrow keys and
move up and down in the list.

Bug: T159768
Change-Id: Ife62e6e7241b96d846d8c5851b173a09a1f45fa4