repl: Set up a way to copy output from the REPL (#16649)

Closes #15494

Simple copy button to copy an individual output since selection is a bit
more work.

<img width="790" alt="image"
src="https://github.com/user-attachments/assets/4a7d8b69-70cc-428e-8fe3-b95386d341ee">


Release Notes:

- repl: Copy output from the REPL using a button

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/gpui/src/assets.rs

@@ -30,7 +30,7 @@ impl AssetSource for () {
 
 /// A unique identifier for the image cache
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
-pub struct ImageId(usize);
+pub struct ImageId(pub usize);
 
 #[derive(PartialEq, Eq, Hash, Clone)]
 pub(crate) struct RenderImageParams {