fix Pyrefly rejects duck-typed Mapping when unpacking in dict #4813

[asukaminato0721]

Summary

Fixes #4813

dictionary unpacking now accepts compatible keys() and __getitem__() methods without requiring Mapping inheritance.

Test Plan

add test

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D118851422. (Because this pull request was imported automatically, there will not be any future comments.)

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

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SUMMARY
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Total: +0 new errors, -5 fixed errors
By preset: +0/-5 (default), +0/-5 (strict)

Projects with changes (2):
  cki-lib: +0 -1
  ibis: +0 -4
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FULL DIFF DETAILS
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cki-lib (https://gitlab.com/cki-project/cki-lib)
- ERROR cki_lib/inttests/remote_responses.py:241:80-92: Expected a mapping, got Message [invalid-argument]

ibis (https://github.com/ibis-project/ibis)
- ERROR ibis/common/collections.py:263:20-24: Expected a mapping, got Self@MapSet [invalid-argument]
- ERROR ibis/common/collections.py:272:20-24: Expected a mapping, got Self@MapSet [invalid-argument]
- ERROR ibis/common/collections.py:272:28-33: Expected a mapping, got Self@MapSet [invalid-argument]
- ERROR ibis/expr/types/relations.py:934:32-38: Expected a mapping, got Schema [invalid-argument]