in the program
```python
if not is_safe(path):
return
```
the last node in the `ConditionBlock` is `not is_safe(path)`,
so it would never match "a call to is_safe".
Thus, guards inside `not` would not be part of `GuardNode`
(nor `BarrierGuard`). Now they can.
Along with the root cause, which is the `StringConstCompare`
BarrierGuard, that does only allows `in <iterable literal>` and not
`in <variable referencing iterable literal>`
The meat of this PR is described in the new python/ql/test/experimental/meta/InlineTaintTest.qll file:
> Defines a InlineExpectationsTest for checking whether any arguments in
> `ensure_tainted` and `ensure_not_tainted` calls are tainted.
>
> Also defines query predicates to ensure that:
> - if any arguments to `ensure_not_tainted` are tainted, their annotation is marked with `SPURIOUS`.
> - if any arguments to `ensure_tainted` are not tainted, their annotation is marked with `MISSING`.
>
> The functionality of this module is tested in `ql/test/experimental/meta/inline-taint-test-demo`.
