Since predicate name `import` is not allowed, I adopted `importNode` as it sort
of matches what `exprNode` does.
---
Due to only using `importMember` in `os_attr` we previously didn't handle
`import os.path as alias` :|
I did creat a hotfix for this (https://github.com/github/codeql/pull/4446), but
in doing so I realized the core of the problem: We're exposing ourselves to
making these kinds of mistakes by having BOTH importModule and importMember, and
we don't really gain anything from doing this!
We do loose the ability to easily only modeling `from mod import val` and not
`import mod.val`, but I don't think that will ever be relevant.
This change will also make us to recognize some invalid code, for example in
import os.system as runtime_error
we would now model that `runtime_error` is a reference to the `os.system`
function (although the actual import would result in a runtime error).
Overall these are tradeoffs I'm willing to make, as it does makes things simpler
from a QL modeling point of view, and THAT sounds nice 👍
Required a small change in `DataFlow::importModule` to get the desired
behaviour (cf. the type trackers defined in `moduleattr.ql`, but this
should be harmless. The node that is added doesn't have any flow
anywhere.
