elixir: Improve ElixirLS LSP autocomplete to show labelDetails information (#21666)

Closes https://github.com/zed-industries/zed/issues/19688

Release Notes:

- Improved ElixirLS LSP autocomplete to show module, function and struct
field details

![image](https://github.com/user-attachments/assets/2f05183f-8f7f-42c3-ba14-28fc58522488)

![image](https://github.com/user-attachments/assets/bfdea373-79ec-4dec-a9c7-5d15ad9403ee)

![image](https://github.com/user-attachments/assets/c0fd66d5-0e01-4e1e-a2d5-0a78d38e0b72)