Closes https://github.com/zed-industries/zed/issues/62262

## Solution

Identical hover responses from multiple language servers should be
displayed only once.

Different hover responses should still all be preserved, since multiple
language servers may provide complementary information.


## Showcase



https://github.com/user-attachments/assets/67246d9f-ed1c-4f5a-98f5-f10548b7fc6d



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Release Notes:

- Deduplicated identical language server hover responses

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Signed-off-by: Xiaobo Liu <cppcoffee@gmail.com>
Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>