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/ui/src/components/label/label.rs

@@ -37,7 +37,7 @@ pub struct Label {
 }
 
 impl Label {
-    /// Create a new [`Label`] with the given text.
+    /// Creates a new [`Label`] with the given text.
     ///
     /// # Examples
     ///