Move GraphicSlot out of components module (#3444)

This PR moves the `GraphicSlot` definition out of the `components`
module, as it doesn't contain a component.

Release Notes:

- N/A

crates/ui2/src/components/slot.rs

@@ -1,14 +0,0 @@
-use gpui::{ImageSource, SharedString};
-
-use crate::Icon;
-
-#[derive(Debug, Clone)]
-/// A slot utility that provides a way to to pass either
-/// an icon or an image to a component.
-///
-/// Can be filled with a []
-pub enum GraphicSlot {
-    Icon(Icon),
-    Avatar(ImageSource),
-    PublicActor(SharedString),
-}