Add coarsen, rolling and weighted to generate_reductions

[headtr1ck]

Is your feature request related to a problem?

Coarsen reductions are currently added dynamically which is not very useful for typing.
This is a follow-up to @Illviljan in #6702 (comment)_

Same goes for Weighted.
And similar for Rolling (not sure if it is exactly the same though?)

Describe the solution you'd like

Extend the generate_reductions script to include DataArrayCoarsen and DatasetCoarsen.
Once finished: use type checking in all test_coarsen tests.

[headtr1ck]

For better docstrings (in the editor) the weighted module could be another candidate.
There only the docstrings are added dynamically, so this has a lower priority.