[FEAT] Support textDocument/selectionRange

[shilangyu]

Documented here: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_selectionRange

Demo of this feature using Rust's LSP:

Screen.Recording.2026-07-08.at.16.28.52.mov

A very simple first version could be to expand a selection to the entire sentence. This is exactly what rocq-lsp does. This would be very easy to implement.

In the future, the implementation could be extended to increase selections based on the AST structure (especially in Gallina).

[charst4r]

Hi, I'd like to work on this!