Enable clippy::useless_conversion (#8724)

This PR enables the
[`clippy::useless_conversion`](https://rust-lang.github.io/rust-clippy/master/index.html#/useless_conversion)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/editor/src/scroll.rs

@@ -470,7 +470,7 @@ impl Editor {
                 .buffer()
                 .read(cx)
                 .snapshot(cx)
-                .anchor_at(Point::new(top_row as u32, 0), Bias::Left);
+                .anchor_at(Point::new(top_row, 0), Bias::Left);
             let scroll_anchor = ScrollAnchor {
                 offset: gpui::Point::new(x, y),
                 anchor: top_anchor,