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/terminal_view/src/terminal_view.rs

@@ -991,7 +991,7 @@ impl Item for TerminalView {
             Some(terminal_task) => match &terminal_task.status {
                 TaskStatus::Running => (IconName::Play, Color::Disabled, None),
                 TaskStatus::Unknown => (
-                    IconName::ExclamationTriangle,
+                    IconName::Warning,
                     Color::Warning,
                     Some(rerun_button(terminal_task.id.clone())),
                 ),