Explicitly order CameraUpdateSystem before UiSystem::Prepare (#14609)

# Objective

Fixes https://github.com/bevyengine/bevy/issues/14277.

May also fix https://github.com/bevyengine/bevy/issues/14255, needs
verification.

## Solution

Explicitly order `CameraUpdateSystem` before `UiSystem::Prepare`, so
that when the window resizes, `camera_system` will update the `Camera`'s
viewport size before `ui_layout_system` also reacts to the window resize
and tries to read the new `Camera` viewport size to set UI node sizes
accordingly.

## Testing

I tested that explicitly ordering `CameraUpdateSystem` _after_ triggers
the buggy behavior, and explicitly ordering it _before_ does not trigger
the buggy behavior or crash the app (which also demonstrates that the
system sets are ambiguous).

---

## Migration Guide

`CameraUpdateSystem` is now explicitly ordered before
`UiSystem::Prepare` instead of being ambiguous with it.

crates/bevy_ui/src/lib.rs

@@ -54,6 +54,7 @@ use bevy_app::prelude::*;
 use bevy_ecs::prelude::*;
 use bevy_input::InputSystem;
 use bevy_render::{
+    camera::CameraUpdateSystem,
     view::{check_visibility, VisibilitySystems},
     RenderApp,
 };
@@ -146,6 +147,7 @@ impl Plugin for UiPlugin {
             .configure_sets(
                 PostUpdate,
                 (
+                    CameraUpdateSystem,
                     UiSystem::Prepare.before(UiSystem::Stack),
                     UiSystem::Layout,
                     (UiSystem::PostLayout, UiSystem::Outlines),
@@ -226,11 +228,6 @@ fn build_text_interop(app: &mut App) {
             widget::measure_text_system
                 .in_set(UiSystem::Prepare)
                 // Potential conflict: `Assets<Image>`
-                // In practice, they run independently since `bevy_render::camera_update_system`
-                // will only ever observe its own render target, and `widget::measure_text_system`
-                // will never modify a pre-existing `Image` asset.
-                .ambiguous_with(bevy_render::camera::CameraUpdateSystem)
-                // Potential conflict: `Assets<Image>`
                 // 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)

tests/ecs/ambiguity_detection.rs

@@ -69,7 +69,7 @@ pub fn main() {
 
     let total_ambiguities = ambiguities.total();
     assert_eq!(
-        total_ambiguities, 81,
+        total_ambiguities, 72,
         "Main app does not have an expected conflicting systems count, \
         you might consider verifying if it's normal, or change the expected number.\n\
         Details:\n{:#?}",