ART: Improve range search caching in LiveInterval

Register allocator spends too long in LiveInterval queries. This patch
builds on previously introduced caching of range search results to
further speed up LiveInterval's Covers and FindIntersectionWith.
Only calls which are guaranteed to query the current->GetStart()
position are cached. Other calls are replaced with CoversSlow which
searches through the entire list of ranges.

Change-Id: I84d92b526e174caa70d6477497a06afd85016c4a