Prefer .map for conditionals with else conditions (#15118)

This PR updates instances where we were using `.when_else` and
`.when_else_some` to use `.map` with a conditional inside.

This allows us to avoid reinventing Rust's syntax for conditionals and
(IMO) makes the code easier to read.

Release Notes:

- N/A

crates/workspace/src/toolbar.rs

@@ -119,9 +119,15 @@ impl Render for Toolbar {
                     .when(has_right_items, |this| {
                         this.child(
                             h_flex()
-                                // We're using `flex_none` here to prevent some flickering that can occur when the
-                                // size of the left items container changes.
-                                .when_else(has_left_items, Div::flex_none, Div::flex_auto)
+                                .map(|el| {
+                                    if has_left_items {
+                                        // We're using `flex_none` here to prevent some flickering that can occur when the
+                                        // size of the left items container changes.
+                                        el.flex_none()
+                                    } else {
+                                        el.flex_auto()
+                                    }
+                                })
                                 .justify_end()
                                 .children(self.right_items().map(|item| item.to_any())),
                         )