* Brings back hover popover of selection context.

* Adds hover popover for symbol, rules, and thread context.

* Makes context attached to messages display the names / content at
attachment time.

* Adds the file name as the displayed parent of symbol context.

* Brings back `impl Component for AddedContext`

Release Notes:

- N/A

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Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>