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/activity_indicator/src/activity_indicator.rs

@@ -262,7 +262,7 @@ impl ActivityIndicator {
         if !failed.is_empty() {
             return Some(Content {
                 icon: Some(
-                    Icon::new(IconName::ExclamationTriangle)
+                    Icon::new(IconName::Warning)
                         .size(IconSize::Small)
                         .into_any_element(),
                 ),
@@ -280,7 +280,7 @@ impl ActivityIndicator {
         if let Some(failure) = self.project.read(cx).last_formatting_failure() {
             return Some(Content {
                 icon: Some(
-                    Icon::new(IconName::ExclamationTriangle)
+                    Icon::new(IconName::Warning)
                         .size(IconSize::Small)
                         .into_any_element(),
                 ),
@@ -333,7 +333,7 @@ impl ActivityIndicator {
                 }),
                 AutoUpdateStatus::Errored => Some(Content {
                     icon: Some(
-                        Icon::new(IconName::ExclamationTriangle)
+                        Icon::new(IconName::Warning)
                             .size(IconSize::Small)
                             .into_any_element(),
                     ),