Note that in this case, since there is a known `django.urls.path`
route-setup, we know that the request-handler will only be passed
keyword arguments, so it is not a mistake that `*args` is not considered
a routed-parameter here (although it certainly wouldn't have hurt us if
we did consider it a routed-parameter either).
This commit removes SSA nodes from the data flow graph. Specifically, for a definition and use such as
```python
x = expr
y = x + 2
```
we used to have flow from `expr` to an SSA variable representing x and from that SSA variable to the use of `x` in the definition of `y`. Now we instead have flow from `expr` to the control flow node for `x` at line 1 and from there to the control flow node for `x` at line 2.
Specific changes:
- `EssaNode` from the data flow layer no longer exists.
- Several glue steps between `EssaNode`s and `CfgNode`s have been deleted.
- Entry nodes are now admitted as `CfgNodes` in the data flow layer (they were filtered out before).
- Entry nodes now have a new `toString` taking into account that the module name may be ambigous.
- Some tests have been rewritten to accomodate the changes, but only `python/ql/test/experimental/dataflow/basic/maximalFlowsConfig.qll` should have semantic changes.
- Comments have been updated
- Test output has been updated, but apart from `python/ql/test/experimental/dataflow/basic/maximalFlows.expected` only `python/ql/test/experimental/dataflow/typetracking-summaries/summaries.py` should have a semantic change. This is a bonus fix, probably meaning that something was never connected up correctly.
Mostly to highlight that with flow-summary modeling, we don't expect
taint for a lot of these.
I aslo opted to make `finditer()` tainted for consistency.
Factor out use-use flow in order to do this.
Also improve names and comments.
I also wanted to change the types in `difinitionFlowStep`, but
that broke the module instantiation.
These are semantic differences.
They generally look good, except perhaps
we should exclude illegal package names?
(It passes `legalShortName`, though).
