Really, this boils down to "Port `re` library model to use API graphs
instead of points-to", which is what this PR actually does.
Instead of using points-to to track flags, we use a type tracker. To
handle multiple flags at the same time, we add additional flow from
`x` to `x | y` and `y | x`
and, as an added bonus, the above with `+` instead of `|`, neatly
fixing https://github.com/github/codeql/issues/4707
I had to modify the `Qualified.ql` test slightly, as it now had a
result stemming from the standard library (in `warnings.py`) that
points-to previously ignored.
It might be possible to implement this as a type tracker on
`LocalSourceNode`s, but with the added steps for the above operations,
this was not obvious to me, and so I opted for the simpler
"`smallstep`" variant.
Notice that there is no new results for line 54
I also added a test for the short-named version of a flag, just since I didn't
see any of those already. That just works out of the box (due to points-to).
