[ty] include overload declarations in find references (#23215)
## Summary
Fixes astral-sh/ty/issues/886
Previously, find references/rename did not include the full overload
set. We now correctly provide all overload declarations and the
implementation.
## Test Plan
- Added a `find_references` test for overloaded function declarations
- Updated overloaded rename snapshots to reflect the expected full
overload set
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Co-authored-by: David Peter <mail@david-peter.de>
