Derive icon paths (#17816)

This PR improves adding and working with icons by using the new
`DerivePathStr` to derive icon paths.

This means paths no longer need to be manually specified, and the
`IconName` and file name will always be consistent between icons.

This PR does not do any work to standardize icons visually, remove
unused icons, or any other such cleanup.

Release Notes:

- N/A

crates/diagnostics/src/toolbar_controls.rs

@@ -50,7 +50,7 @@ impl Render for ToolbarControls {
                 )
             })
             .child(
-                IconButton::new("toggle-warnings", IconName::ExclamationTriangle)
+                IconButton::new("toggle-warnings", IconName::Warning)
                     .tooltip(move |cx| Tooltip::text(tooltip, cx))
                     .on_click(cx.listener(|this, _, cx| {
                         if let Some(editor) = this.editor() {