fix(@angular-devkit/build-angular): provide Vite client code source map when loading

The sourcemap for the Vite client code was previously not being loaded along with the
actual code. This could lead to browser 404 console messages when debugging applications.

(cherry picked from commit e98dde6)

Author: clydin

packages/angular_devkit/build_angular/src/tools/vite/angular-memory-plugin.ts

@@ -68,13 +68,16 @@ export function createAngularMemoryPlugin(options: AngularMemoryPluginOptions):
         return join(virtualProjectRoot, source);
       }
     },
-    load(id) {
+    async load(id) {
       const [file] = id.split('?', 1);
       const relativeFile = '/' + normalizePath(relative(virtualProjectRoot, file));
       const codeContents = outputFiles.get(relativeFile)?.contents;
       if (codeContents === undefined) {
         if (relativeFile.endsWith('/node_modules/vite/dist/client/client.mjs')) {
-          return loadViteClientCode(file);
+          return {
+            code: await loadViteClientCode(file),
+            map: await readFile(file + '.map', 'utf-8'),
+          };
         }
 
         return;