Add screenshot check on UI (#16486)

# Objective

- Progress towards #15918 
- Add test on UI

## Solution

- Get a single screenshot from the UI testbed example
- Remove older examples from runs in CI as they're covered by the
testbed to reduce CI duration

.github/example-run/alien_cake_addict.ron

@@ -1,5 +0,0 @@
-(
-    events: [
-        (300, AppExit),
-    ]
-)

.github/example-run/breakout.ron

@@ -1,8 +0,0 @@
-(
-    setup: (
-        fixed_frame_time: Some(0.03),
-    ),
-    events: [
-        (900, AppExit),
-    ]
-)

.github/example-run/testbed_ui.ron

@@ -0,0 +1,6 @@
+(
+    events: [
+        (100, Screenshot),
+        (200, AppExit),
+    ]
+)

.github/workflows/ci.yml

@@ -261,10 +261,6 @@ jobs:
       - name: Disable audio
         # Disable audio through a patch. on github m1 runners, audio timeouts after 15 minutes
         run: git apply --ignore-whitespace tools/example-showcase/disable-audio.patch
-      - name: Build bevy
-        # this uses the same command as when running the example to ensure build is reused
-        run: |
-          TRACE_CHROME=trace-alien_cake_addict.json CI_TESTING_CONFIG=.github/example-run/alien_cake_addict.ron cargo build --example alien_cake_addict --features "bevy_ci_testing,trace,trace_chrome"
       - name: Run examples
         run: |
           for example in .github/example-run/*.ron; do

.github/workflows/validation-jobs.yml

@@ -101,10 +101,6 @@ jobs:
             target/
           key: ${{ runner.os }}-cargo-run-examples-${{ hashFiles('**/Cargo.toml') }}
       - uses: dtolnay/rust-toolchain@stable
-      - name: Build bevy
-        # this uses the same command as when running the example to ensure build is reused
-        run: |
-          TRACE_CHROME=trace-alien_cake_addict.json CI_TESTING_CONFIG=.github/example-run/alien_cake_addict.ron cargo build --example alien_cake_addict --features "bevy_ci_testing,trace,trace_chrome"
       - name: Run examples
         run: |
           for example in .github/example-run/*.ron; do
@@ -155,11 +151,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
-      - name: Build bevy
-        shell: bash
-        # this uses the same command as when running the example to ensure build is reused
-        run: |
-          WGPU_BACKEND=dx12 TRACE_CHROME=trace-alien_cake_addict.json CI_TESTING_CONFIG=.github/example-run/alien_cake_addict.ron cargo build --example alien_cake_addict --features "bevy_ci_testing,trace,trace_chrome"
       - name: Run examples
         shell: bash
         run: |

examples/testbed/ui.rs

@@ -10,14 +10,11 @@ use bevy::{
     picking::focus::HoverMap,
     prelude::*,
     ui::widget::NodeImageMode,
-    winit::WinitSettings,
 };
 
 fn main() {
     let mut app = App::new();
     app.add_plugins(DefaultPlugins)
-        // Only run the app when there is user input. This will significantly reduce CPU/GPU use.
-        .insert_resource(WinitSettings::desktop_app())
         .add_systems(Startup, setup)
         .add_systems(Update, update_scroll_position);