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/collab_ui/src/collab_panel.rs

@@ -2831,7 +2831,7 @@ impl Panel for CollabPanel {
     fn icon(&self, cx: &gpui::WindowContext) -> Option<ui::IconName> {
         CollaborationPanelSettings::get_global(cx)
             .button
-            .then_some(ui::IconName::Collab)
+            .then_some(ui::IconName::UserGroup)
     }
 
     fn icon_tooltip(&self, _cx: &WindowContext) -> Option<&'static str> {