Use more LSP data when falling back to regular completions label (#23909)

Closes https://github.com/zed-industries/zed/issues/23590
Closes https://x.com/steeve/status/1865129235536568555

Before:

<img width="773" alt="before"
src="https://github.com/user-attachments/assets/129a8d12-9298-4bf5-8f2d-b3292c2562bf"
/>


After:

<img width="768" alt="after"
src="https://github.com/user-attachments/assets/e0516fb3-b02a-48be-8923-63bba05fdb69"
/>


The list obviously needs some solution for the cut-off part of the
completion label, but this is the reality for all extensions'
completions too, so one step at a time.


Release Notes:

- Improved default completion label fallback

crates/project/src/lsp_store.rs

@@ -4380,7 +4380,8 @@ impl LspStore {
 
         // NB: Zed does not have `details` inside the completion resolve capabilities, but certain language servers violate the spec and do not return `details` immediately, e.g. https://github.com/yioneko/vtsls/issues/213
         // So we have to update the label here anyway...
-        let mut new_label = match snapshot.language() {
+        let language = snapshot.language();
+        let mut new_label = match language {
             Some(language) => {
                 adapter
                     .labels_for_completions(&[completion_item.clone()], language)
@@ -4391,9 +4392,9 @@ impl LspStore {
         .pop()
         .flatten()
         .unwrap_or_else(|| {
-            CodeLabel::plain(
-                completion_item.label,
-                completion_item.filter_text.as_deref(),
+            CodeLabel::fallback_for_completion(
+                &completion_item,
+                language.map(|language| language.as_ref()),
             )
         });
         ensure_uniform_list_compatible_label(&mut new_label);
@@ -8079,10 +8080,7 @@ async fn populate_labels_for_completions(
         };
 
         let mut label = label.unwrap_or_else(|| {
-            CodeLabel::plain(
-                lsp_completion.label.clone(),
-                lsp_completion.filter_text.as_deref(),
-            )
+            CodeLabel::fallback_for_completion(&lsp_completion, language.as_deref())
         });
         ensure_uniform_list_compatible_label(&mut label);
 
@@ -8883,7 +8881,7 @@ fn include_text(server: &lsp::LanguageServer) -> Option<bool> {
 /// Completion items are displayed in a `UniformList`.
 /// Usually, those items are single-line strings, but in LSP responses,
 /// completion items `label`, `detail` and `label_details.description` may contain newlines or long spaces.
-/// Many language plugins construct these items by joining these parts together, and we may fall back to `CodeLabel::plain` that uses `label`.
+/// Many language plugins construct these items by joining these parts together, and we may use `CodeLabel::fallback_for_completion` that uses `label` at least.
 /// All that may lead to a newline being inserted into resulting `CodeLabel.text`, which will force `UniformList` to bloat each entry to occupy more space,
 /// breaking the completions menu presentation.
 ///