Use thread/iteration safe collection for proximity listeners

CopyOnWrite datastructures essentially do what the existing code did: they ensure that iteration operates on an immutable copy of the list and never throw ConcurrentModificationException. They're also more efficient because they do copy only on add, not each iteration.

Bug: 354293532
Test: atest ProximitySensorImplDualTest ProximitySensorImplSingleTest
Flag: EXEMPT inplace refactor
Change-Id: If687969a7ef81e33e8f41b28a751ca60fd90349f