Enable clangd's dot-to-arrow feature (#21142)

Closes #20815


![dot2arrow1127](https://github.com/user-attachments/assets/d825f9bf-52ae-47ee-b3a3-5f952b6e8979)

Release Notes:
- Enabled clangd's dot-to-arrow feature

crates/languages/src/c.rs

@@ -4,10 +4,11 @@ use futures::StreamExt;
 use gpui::AsyncAppContext;
 use http_client::github::{latest_github_release, GitHubLspBinaryVersion};
 pub use language::*;
-use lsp::{LanguageServerBinary, LanguageServerName};
+use lsp::{InitializeParams, LanguageServerBinary, LanguageServerName};
+use serde_json::json;
 use smol::fs::{self, File};
 use std::{any::Any, env::consts, path::PathBuf, sync::Arc};
-use util::{fs::remove_matching, maybe, ResultExt};
+use util::{fs::remove_matching, maybe, merge_json_value_into, ResultExt};
 
 pub struct CLspAdapter;
 
@@ -257,6 +258,26 @@ impl super::LspAdapter for CLspAdapter {
             filter_range,
         })
     }
+
+    fn prepare_initialize_params(
+        &self,
+        mut original: InitializeParams,
+    ) -> Result<InitializeParams> {
+        // enable clangd's dot-to-arrow feature.
+        let experimental = json!({
+            "textDocument": {
+                "completion" : {
+                    "editsNearCursor": true
+                }
+            }
+        });
+        if let Some(ref mut original_experimental) = original.capabilities.experimental {
+            merge_json_value_into(experimental, original_experimental);
+        } else {
+            original.capabilities.experimental = Some(experimental);
+        }
+        Ok(original)
+    }
 }
 
 async fn get_cached_server_binary(container_dir: PathBuf) -> Option<LanguageServerBinary> {