Allow bevy_ui crate to compile without the text feature enabled (#8437)

# Objective

Allow `bevy_ui` crate to compile without the `text` feature enabled

## Solution

- Correctly conditionally compile `text_system`

crates/bevy_ui/src/lib.rs

@@ -124,6 +124,7 @@ impl Plugin for UiPlugin {
         #[cfg(feature = "bevy_text")]
         app.add_systems(
             PostUpdate,
+            (
                 widget::measure_text_system
                     .before(UiSystem::Layout)
                     // Potential conflict: `Assets<Image>`
@@ -135,6 +136,8 @@ impl Plugin for UiPlugin {
                     // Since both systems will only ever insert new [`Image`] assets,
                     // they will never observe each other's effects.
                     .ambiguous_with(bevy_text::update_text2d_layout),
+                widget::text_system.after(UiSystem::Layout),
+            ),
         );
         #[cfg(feature = "bevy_text")]
         app.add_plugin(accessibility::AccessibilityPlugin);
@@ -159,7 +162,6 @@ impl Plugin for UiPlugin {
                     .before(TransformSystem::TransformPropagate),
                 ui_stack_system.in_set(UiSystem::Stack),
                 update_clipping_system.after(TransformSystem::TransformPropagate),
-                widget::text_system.after(UiSystem::Layout),
             ),
         );