lsp: Track completion triggers for each language separately (#20471)

This PR improves how we handle completions in buffers with multiple
LSPs.

Context: while working on
https://github.com/zed-industries/zed/issues/19777 with @mgsloan we
noticed that completion triggers coming from language servers are not
tracked properly. Namely, each buffer has `completion_triggers` field
which is read from the configuration of a language server. The problem
is, there can be multiple language servers for a single buffer, in which
case we'd just stick to the one that was registered last.

This PR makes the tracking a bit more fine-grained. We now track not
only what the completion triggers are, but also their origin server id.
Whenever completion triggers are updated, we recreate the completion
triggers set.
Release Notes:

- Fixed completions not triggering when multiple language servers are
used for a single file.

crates/project/src/project_tests.rs

@@ -481,7 +481,11 @@ async fn test_managing_language_servers(cx: &mut gpui::TestAppContext) {
     // The buffer is configured based on the language server's capabilities.
     rust_buffer.update(cx, |buffer, _| {
         assert_eq!(
-            buffer.completion_triggers(),
+            buffer
+                .completion_triggers()
+                .into_iter()
+                .cloned()
+                .collect::<Vec<_>>(),
             &[".".to_string(), "::".to_string()]
         );
     });
@@ -528,7 +532,14 @@ async fn test_managing_language_servers(cx: &mut gpui::TestAppContext) {
     // This buffer is configured based on the second language server's
     // capabilities.
     json_buffer.update(cx, |buffer, _| {
-        assert_eq!(buffer.completion_triggers(), &[":".to_string()]);
+        assert_eq!(
+            buffer
+                .completion_triggers()
+                .into_iter()
+                .cloned()
+                .collect::<Vec<_>>(),
+            &[":".to_string()]
+        );
     });
 
     // When opening another buffer whose language server is already running,
@@ -541,7 +552,11 @@ async fn test_managing_language_servers(cx: &mut gpui::TestAppContext) {
         .unwrap();
     rust_buffer2.update(cx, |buffer, _| {
         assert_eq!(
-            buffer.completion_triggers(),
+            buffer
+                .completion_triggers()
+                .into_iter()
+                .cloned()
+                .collect::<Vec<_>>(),
             &[".".to_string(), "::".to_string()]
         );
     });