Fix completion labels becoming overly large due to LSP completion items with newlines (#23407)

Reworks https://github.com/zed-industries/zed/pull/23030 and
https://github.com/zed-industries/zed/pull/15087
Closes https://github.com/zed-industries/zed/issues/23352
Closes https://github.com/zed-industries/zed/issues/23310 

Zed's completion items use `label` from LSP completion items as a base
to show in the list:
d290da7dac/crates/project/src/lsp_store.rs (L4371-L4374)

Besides that, certain language plugins append `detail` or
`label_details.description` as a suffix:
d290da7dac/crates/languages/src/vtsls.rs (L178-L188)

Either of these 3 properties may return `\n` (or multiple) in it,
spoiling Zed's completion menu, which uses `UniformList` to render those
items: a uniform list uses common, minimum possible height for each
element, and `\n` bloats that overly.

Good approach would be to use something else:
https://github.com/zed-industries/zed/issues/21403 but that has its own
drawbacks and relatively hard to use instead (?).

We could follow VSCode's approach and move away all but `label` from
`CodeLabel.text` to the side, where the documentation is, but that does
not solve the issue with `details` having newlines.

So, for now, sanitize all labels and remove any newlines from them. If
newlines are found, also replace whitespace sequences if there's more
than 1 in a row.

Later, this approach can be improved similarly to how Helix and Zed's
inline completions do: rendering a "ghost" text, showing the
completion's edit applied to the editor.

Release Notes:

- Fixed completion labels becoming overly large due to LSP completion
items with newlines

crates/language/src/language.rs

@@ -763,6 +763,14 @@ pub struct FakeLspAdapter {
 
     pub capabilities: lsp::ServerCapabilities,
     pub initializer: Option<Box<dyn 'static + Send + Sync + Fn(&mut lsp::FakeLanguageServer)>>,
+    pub label_for_completion: Option<
+        Box<
+            dyn 'static
+                + Send
+                + Sync
+                + Fn(&lsp::CompletionItem, &Arc<Language>) -> Option<CodeLabel>,
+        >,
+    >,
 }
 
 /// Configuration of handling bracket pairs for a given language.
@@ -1778,6 +1786,7 @@ impl Default for FakeLspAdapter {
                 arguments: vec![],
                 env: Default::default(),
             },
+            label_for_completion: None,
         }
     }
 }
@@ -1849,6 +1858,15 @@ impl LspAdapter for FakeLspAdapter {
     ) -> Result<Option<Value>> {
         Ok(self.initialization_options.clone())
     }
+
+    async fn label_for_completion(
+        &self,
+        item: &lsp::CompletionItem,
+        language: &Arc<Language>,
+    ) -> Option<CodeLabel> {
+        let label_for_completion = self.label_for_completion.as_ref()?;
+        label_for_completion(item, language)
+    }
 }
 
 fn get_capture_indices(query: &Query, captures: &mut [(&str, &mut Option<u32>)]) {