Improve outline panel performance (#17183)

Part of https://github.com/zed-industries/zed/issues/14235

* moved search results highlight calculation into the background thread,
with highlight-less representation as a fallback
* show only a part of the line per search result, stop uniting them into
a single line if possible, always trim left trailing whitespaces
* highlight results in batches
* better cache all search result data, related to rendering
* add test infra and fix folding-related issues
* improve entry displays when multi buffer has a buffer search (find
references one has)
* fix cloud notes not showing search matches

Release Notes:

- Improved outline panel performance

crates/workspace/src/pane.rs

@@ -118,7 +118,7 @@ pub struct RevealInProjectPanel {
     pub entry_id: Option<u64>,
 }
 
-#[derive(PartialEq, Clone, Deserialize)]
+#[derive(Default, PartialEq, Clone, Deserialize)]
 pub struct DeploySearch {
     #[serde(default)]
     pub replace_enabled: bool,