Update tenses of doc comment summary lines (#4161)

This PR updates the tenses used by the summary line of doc comments to
match the [Rust API documentation
conventions](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#summary-sentence).

Specifically:

> The summary line should be written in third person singular present
indicative form. Basically, this means write ‘Returns’ instead of
‘Return’.

I'm sure there are plenty occurrences that I missed.

Release Notes:

- N/A

crates/terminal_view/src/terminal_view.rs

@@ -832,7 +832,7 @@ impl SearchableItem for TerminalView {
         self.terminal().update(cx, |term, _| term.matches = matches)
     }
 
-    /// Return the selection content to pre-load into this search
+    /// Returns the selection content to pre-load into this search
     fn query_suggestion(&mut self, cx: &mut ViewContext<Self>) -> String {
         self.terminal()
             .read(cx)