Sorting search results with TreeSet instead of Collection.sort

Benchmarking shows lower sorting latencies with with TreeSet, specially
with larger lists:

Average Latencies(ms):
                  list size in [0, 115]         list size in [40, 115]
Collection.sort   39.22                         77.57
TreeSet           30.23                         52.06

Test: RunSettingsRoboTests

Bug: 38197948
Bug: 37312700

Change-Id: I1dd7c77900e8e98e26a8417f2b77582532e1a5f3