In a collapsed hierarchy, some type of data are listed as one icon per item (2.79 did this for all data),
others are 'compacted' as a single icon with a counter (also indicating if the active item is down that collapsed hierarchy) from 2.80 on.
Not quite sure if rB92dfc8f2673e: Outliner: regroup more type of entries under a single icon. was meant to do this (if it was, this
was not working though because relevant code would only get executed for
object hierarchies it seems), so now this is done for bones as well.
Fixes T88413.

