ui: Add margin style methods to Label and LabelLike (#14032)

This PR adds margin style methods to the `Label` and `LabelLike`
components.

This allows for callers to provide a margin to these components without
needing to introduce a wrapping `div` to do so.

Release Notes:

- N/A

crates/title_bar/src/collab.rs

@@ -262,9 +262,8 @@ impl TitleBar {
                         ))
                         .children(if extra_count > 0 {
                             Some(
-                                div()
+                                Label::new(format!("+{extra_count}"))
                                     .ml_1()
-                                    .child(Label::new(format!("+{extra_count}")))
                                     .into_any_element(),
                             )
                         } else {