[BasicAA] Move assumption tracking into AAQI

D91936 placed the tracking for the assumptions into BasicAA.
However, when recursing over phis, we may use fresh AAQI instances.
In this case AssumptionBasedResults from an inner AAQI can reesult
in a removal of an element from the outer AAQI.

To avoid this, move the tracking into AAQI. This generally makes
more sense, as the NoAlias assumptions themselves are also stored
in AAQI.

The test case only produces an assertion failure with D90094
reapplied. I think the issue exists independently of that change
as well, but I wasn't able to come up with a reproducer.