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/quick_action_bar/src/quick_action_bar.rs

@@ -150,7 +150,7 @@ impl Render for QuickActionBar {
             let focus = editor.focus_handle(cx);
             PopoverMenu::new("editor-selections-dropdown")
                 .trigger(
-                    IconButton::new("toggle_editor_selections_icon", IconName::TextCursor)
+                    IconButton::new("toggle_editor_selections_icon", IconName::CursorIBeam)
                         .shape(IconButtonShape::Square)
                         .icon_size(IconSize::Small)
                         .style(ButtonStyle::Subtle)