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.
This detects cases where module A imports a function from B, and C
imports that same function from A instead of B. It's not part of the API
contract of A, and causes innocent refactoring to break things.
D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082