[red-knot] Infer target types for unpacked tuple assignment

[dhruvmanila]

Summary

Test Plan

[dhruvmanila]

There's some more work needs to be done, please don't look ;)

[github-actions]

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[dhruvmanila]

This is completely an incorrect solution, I quickly realize that this will require structural matching between the target expression and the value type. It would also be good to add caching here because we've definitions for each name node on the LHS and so we'd perform structural matching against the same target and value type for each name node that's present on the LHS.