Use t.Mapping not t.Dict for parameters

[altendky]

https://docs.python.org/3/library/typing.html#typing.Dict

To annotate arguments it is preferred to use an abstract collection type such as Mapping.

This PR does almost that to fix the issue below. I instead use MutableMapping here since we do mutate in some cases. I chose to use MutableMapping everywhere for consistency and leaving it open for more mutation in the future. I understand that this may not be preferred and would be happy to use Mapping where possible instead.

• fixes Unable to properly inherit and hint Group due to use of Dict for parameters #2264

It was suggested I could follow #2256 as a guide for how much of this checklist applies to hint-only changes. As such some have been skipped.

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[saroad2]

Hey @altendky , Thanks for the PR and sorry for the long delay!

This PR makes sense to me. I fixed some merging issues and we are ready to merge.
The only thing that I think worth fine tuning is the change note. I wrote a suggestion, but if you have better one - please feel free to paraphrase.

After this is fixed, we could merge!

[altendky]

Your suggestion reads well to me. Thanks for your interest and effort on this.

[saroad2]

I'm now rethinking that this PR might should be merged into 8.1.x instead of main.

@davidism , I would appriciate your input on it.

[davidism]

Yes, this can go in 8.1.x.

[saroad2]

I changed the target branch and reworked the commits history. This is now ready to be merged.

Thanks @altendky again for the PR. I hope to see more of your contributions and the future.