## Summary
This change resolves#15814 to ensure that `SIM401` is only triggered on
known dictionary types. Before, the rule was getting triggered even on
types that _resemble_ a dictionary but are not actually a dictionary.
I did this using the `is_known_to_be_of_type_dict(...)` functionality.
The logic for this function was duplicated in a few spots, so I moved
the code to a central location, removed redundant definitions, and
updated existing calls to use the single definition of the function!
## Test Plan
Since this PR only modifies an existing rule, I made changes to the
existing test instead of adding new ones. I made sure that `SIM401` is
triggered on types that are clearly dictionaries and that it's not
triggered on a simple custom dictionary-like type (using a modified
version of [the code in the issue](#15814))
The additional changes to de-duplicate `is_known_to_be_of_type_dict`
don't break any existing tests -- I think this should be fine since the
logic remains the same (please let me know if you think otherwise, I'm
excited to get feedback and work towards a good fix 🙂).
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Co-authored-by: Junhson Jean-Baptiste <junhsonjb@naan.mynetworksettings.com>
Co-authored-by: Micha Reiser <micha@reiser.io>
