Renaming does not correctly deal with namespaces

Description

#2462 added support for renaming, but the current implementation does not correctly deal with namespaces:

namespace Bar

  structure Foo where
    a : Nat

  def foobar (f : Foo) : Foo := f

end Bar

def foobar (f : Bar.Foo) : Bar.Foo := f

Renaming Foo here breaks references to Bar.Foo. Similarly, when you rename a type, it does not rename the corresponding namespace, leading to errors because dot notation is suddenly broken for a lot of functions.

Context

Prior discussion in the review comments for #2462.

Steps to Reproduce

1. Use the MWE above.
2. Rename Foo.
3. Observe incorrect renaming behaviour.

Expected behavior: Renaming is aware of namespaces.

Actual behavior: Renaming is not aware of namespaces.

Versions

Commit b97b0ad2aaea49a2db3ac0543443ec72bd97dfdc

Impact

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Start with the renaming implementation introduced by #2462 and review the discussion in that change. Reproduce the issue using the MWE, then trace how references to Bar.Foo and its corresponding namespace are handled; done means renaming preserves those references and dot notation without errors.