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/collab/src/tests/random_project_collaboration_tests.rs

@@ -14,7 +14,9 @@ use language::{
 };
 use lsp::FakeLanguageServer;
 use pretty_assertions::assert_eq;
-use project::{search::SearchQuery, Project, ProjectPath, SearchResult};
+use project::{
+    search::SearchQuery, Project, ProjectPath, SearchResult, DEFAULT_COMPLETION_CONTEXT,
+};
 use rand::{
     distributions::{Alphanumeric, DistString},
     prelude::*,
@@ -829,7 +831,7 @@ impl RandomizedTest for ProjectCollaborationTest {
                         .map_ok(|_| ())
                         .boxed(),
                     LspRequestKind::Completion => project
-                        .completions(&buffer, offset, cx)
+                        .completions(&buffer, offset, DEFAULT_COMPLETION_CONTEXT, cx)
                         .map_ok(|_| ())
                         .boxed(),
                     LspRequestKind::CodeAction => project