This changes the schema of the trigger file.
Previously there were too many options and it was confusing. My fault,
sorry.
This meant that `db.execute(query, **TAINT)` was marked as a
vulnerability whereas `db.execute(text=query, **TAINT)` wasn't.
Neither are vulnerabilities, so this gave a FALSE POSITIVE.
Now we have `arg_dict` which is a dictionary of keyword to argument
position.
E.g. for `def f(a, b, *, c)` we can specify the arg_dict as:
```
{"a": 0, "b": 1, "c": null}
```
if we want them all to propagate or not propagate depending on the
`unlisted_args_propagate` value.
This way, we can more easily define db.execute as:
```
 "execute(": {
 "unlisted_args_propagate": false,
 "arg_dict": {
 "text": 0
 }
 },
```

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