Deprecate and remove the experimental CoreApp APIs and prototype app (#…

…12730)

## Description

Deprecated and removed the experimental CoreApp APIs and prototype app. The APIs will no longer be available.

### Type of Change
- Breaking change (fix or feature that would cause existing functionality to not work as expected)

### Why
The experiment was made when we were considering going in a different direction for Fabric-based apps.

Resolves #12617 

### What
See above.

## Screenshots
N/A

## Testing
N/A

## Changelog
Should this change be included in the release notes: _yes_

Deprecated and removed the experimental CoreApp APIs and prototype app

.ado/jobs/playground.yml

@@ -47,10 +47,6 @@ parameters:
             BuildConfiguration: Release
             BuildPlatform: x64
             SolutionFile: Playground-Win32.sln
-          - Name: X64DebugCoreApp
-            BuildConfiguration: Debug
-            BuildPlatform: x64
-            SolutionFile: ..\CoreApp\CoreApp.sln
       - BuildEnvironment: SecurePullRequest
         Matrix:
           - Name: X86DebugCompositionExperimentalWinUI3
@@ -113,10 +109,6 @@ parameters:
             BuildConfiguration: Release
             BuildPlatform: x64
             SolutionFile: Playground-Win32.sln
-          - Name: X64DebugCoreApp
-            BuildConfiguration: Debug
-            BuildPlatform: x64
-            SolutionFile: ..\CoreApp\CoreApp.sln
 
 jobs:
   - ${{ each config in parameters.buildMatrix }}:

change/react-native-windows-f4f321ae-d8bc-4039-8445-aaed6b93d610.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Deprecate and remove CoreApp experiment",
+  "packageName": "react-native-windows",
+  "email": "jthysell@microsoft.com",
+  "dependentChangeType": "patch"
+}

packages/playground/.gitignore

@@ -94,4 +94,3 @@ packages/
 windows/playground/Bundle
 windows/playground-composition/Bundle
 windows/playground-win32/Bundle
-CoreApp/Bundle