feat(@angular-devkit/build-angular): add ng-server-context when using app-shell builder

With this change we configure the app-shell builder to set the `ɵSERVER_CONTEXT` private provider.

Author: alan-agius4

packages/angular_devkit/build_angular/src/builders/app-shell/app-shell_spec.ts

@@ -140,7 +140,8 @@ describe('AppShell Builder', () => {
 
     const fileName = 'dist/index.html';
     const content = virtualFs.fileBufferToString(host.scopedSync().read(normalize(fileName)));
-    expect(content).toMatch(/Welcome to app!/);
+    expect(content).toMatch('Welcome to app');
+    expect(content).toMatch('ng-server-context="app-shell"');
   });
 
   it('works with route', async () => {

packages/angular_devkit/build_angular/src/builders/app-shell/index.ts

@@ -13,6 +13,9 @@ import {
   targetFromTargetString,
 } from '@angular-devkit/architect';
 import { JsonObject } from '@angular-devkit/core';
+import type { Type } from '@angular/core';
+import type * as platformServer from '@angular/platform-server';
+import assert from 'assert';
 import * as fs from 'fs';
 import * as path from 'path';
 import { normalizeOptimization } from '../../utils';
@@ -74,24 +77,28 @@ async function _renderUniversal(
       localeDirectory,
     );
 
-    const { AppServerModule, renderModule } = await import(serverBundlePath);
+    const { AppServerModule, renderModule, ɵSERVER_CONTEXT } = (await import(serverBundlePath)) as {
+      renderModule: typeof platformServer.renderModule | undefined;
+      ɵSERVER_CONTEXT: typeof platformServer.ɵSERVER_CONTEXT | undefined;
+      AppServerModule: Type<unknown> | undefined;
+    };
 
-    const renderModuleFn: ((module: unknown, options: {}) => Promise<string>) | undefined =
-      renderModule;
-
-    if (!(renderModuleFn && AppServerModule)) {
-      throw new Error(
-        `renderModule method and/or AppServerModule were not exported from: ${serverBundlePath}.`,
-      );
-    }
+    assert(renderModule, `renderModule method was not exported from: ${serverBundlePath}.`);
+    assert(AppServerModule, `AppServerModule method was not exported from: ${serverBundlePath}.`);
+    assert(ɵSERVER_CONTEXT, `ɵSERVER_CONTEXT method was not exported from: ${serverBundlePath}.`);
 
     // Load platform server module renderer
-    const renderOpts = {
+    let html = await renderModule(AppServerModule, {
       document: indexHtml,
       url: options.route,
-    };
+      extraProviders: [
+        {
+          provide: ɵSERVER_CONTEXT,
+          useValue: 'app-shell',
+        },
+      ],
+    });
 
-    let html = await renderModuleFn(AppServerModule, renderOpts);
     // Overwrite the client index file.
     const outputIndexPath = options.outputIndexPath
       ? path.join(root, options.outputIndexPath)