Adjust multibuffer header fold button size (#27253)

This PR adjust the size of the fold button on the multibuffer header.
Had to make the `height` method public on the Button Like to pull that
off without other major changes.

| Before | After |
|--------|--------|
| ![CleanShot 2025-03-21 at 12  11
40@2x](https://github.com/user-attachments/assets/003b2965-b1cc-43ad-8528-2bd11cf0f9cc)
| ![CleanShot 2025-03-21 at 12  11
28@2x](https://github.com/user-attachments/assets/d4927b72-3f41-4c4b-9813-49e676170419)
|

Release Notes:

- N/A

crates/ui/src/components/button/button_like.rs

@@ -398,7 +398,7 @@ impl ButtonLike {
         self
     }
 
-    pub(crate) fn height(mut self, height: DefiniteLength) -> Self {
+    pub fn height(mut self, height: DefiniteLength) -> Self {
         self.height = Some(height);
         self
     }