lsp: Provide completion reason in the request (#12893)

This should help LS make a better call about the completions it should
return back to the caller. For example, it speeds up import completions
for typescript.
Before: 


https://github.com/zed-industries/zed/assets/24362066/b38fd565-f9ff-4db7-a87f-c3b31a9fdc96

after: 


https://github.com/zed-industries/zed/assets/24362066/d4fbc9ae-9aab-4543-b9f6-16acf1619576


This should be merged after 06.12 Preview to give it some time on
Nightly.

Release Notes:

- N/A

crates/extension/src/extension_store_test.rs

@@ -15,7 +15,7 @@ use http::{FakeHttpClient, Response};
 use language::{LanguageMatcher, LanguageRegistry, LanguageServerBinaryStatus, LanguageServerName};
 use node_runtime::FakeNodeRuntime;
 use parking_lot::Mutex;
-use project::Project;
+use project::{Project, DEFAULT_COMPLETION_CONTEXT};
 use serde_json::json;
 use settings::{Settings as _, SettingsStore};
 use std::{
@@ -657,7 +657,9 @@ async fn test_extension_store_with_gleam_extension(cx: &mut TestAppContext) {
     });
 
     let completion_labels = project
-        .update(cx, |project, cx| project.completions(&buffer, 0, cx))
+        .update(cx, |project, cx| {
+            project.completions(&buffer, 0, DEFAULT_COMPLETION_CONTEXT, cx)
+        })
         .await
         .unwrap()
         .into_iter()