ART: Move CHA to ClassLinker

Move the ClassHierarchyAnalysis singleton to ClassLinker. Hierarchy
analysis is a link-time effort and belongs to class-loading instead
of the global Runtime object.

Also clean up to use a unique_ptr, and add null checks to allow
bypassing the analysis.

Bug: 34193647
Test: m test-art-host
Change-Id: I14ef536e37eb19c0dede372ffd68a826c482cf71