If an annotation could not be resolved, it's classified as a "missing
import" and our configuration ignored it:
```
Skipping analyzing "mesonbuild.backends": module is installed, but missing library stubs or py.typed marker
```
As far as mypy is concerned, this library may or may not exist, but it
doesn't have any typing information at all (may need to be installed
first).
We ignored this because of our docs/ and tools/ thirdparty dependencies,
but we really should not. It is trivial to install them, and then
enforce that this "just works".
By enforcing it, we also make sure typos get caught.
Regressed in commit bfb12222c3.
This needs to iterate over all methods, process them, and add them to a
list. Instead, it deleted all methods, processed all remaining methods,
and appended them to the in-use iterator.
Use a second list, instead.
Fixes#9922
