Feature Request: type annotations for attributes

[kopp]

When accessing attributes (e.g. the geometry of some feature via some_feature.geometry) it helps if those attributes are modeled in the type system. Then IDEs and tools like mypy can pick up those type hints and provide auto completion or help to avoid issues.

See the following screenshot for an example of IDE support:

This proposal is similar to #167 but proposes to annotate the attribute-access rather than the key-access.

It would be a nice addition to #203 .

[kopp]

#235 contains the code changes that were necessary to my IDE (vscode in this case) to propose this.