Rework BitVector tests for index width change.
Rework BitVector tests for index width change.

Changing indexes from uint32_t to size_t requires updating a fair amount
of test code.

apache/lucy,nwellnhof/lucy,apache/lucy,rbevers/lucy,apache/lucy,nwellnhof/lucy,nwellnhof/lucy,rbevers/lucy,apache/lucy,nwellnhof/lucy,rbevers/lucy,nwellnhof/lucy,apache/lucy,rbevers/lucy,rbevers/lucy,rbevers/lucy,rbevers/lucy,nwellnhof/lucy,apache/lucy,nwellnhof/lucy,apache/lucy