runtime: Bitstring implementation for subtype checking (3/4).

Implement the subtype check manipulation of the class hierarchy.
This walks the class hierarchy tree and allocates bitstring values
to each class by encoding the path from the class to the root as a
bitstring.

Used to implement O(1) subtype checking in the subsequent CL.

Test: art/test.py -b -j32 --host --target
Bug: 64692057
Change-Id: I484940bbb3901b56236245cdd4f8f4a8d859f919