fix(@angular/build): normalize karma asset paths before lookup

When handling a request for a configured asset with the application-
based karma unit testing, the asset URL is now normalized to the
executing platform's path format before looking up the asset. This
is required due to the build file paths being based on the underlying
operating system's paths which may not align with a URL's path separator
such as when using Windows.

(cherry picked from commit bd917d9)

Author: clydin

packages/angular/build/src/builders/karma/application_builder.ts

@@ -29,6 +29,7 @@ import { findTests, getTestEntrypoints } from './find-tests';
 import { Schema as KarmaBuilderOptions } from './schema';
 
 const localResolve = createRequire(__filename).resolve;
+const isWindows = process.platform === 'win32';
 
 interface BuildOptions extends ApplicationBuilderInternalOptions {
   // We know that it's always a string since we set it.
@@ -73,7 +74,14 @@ class AngularAssetsMiddleware {
     let err = null;
     try {
       const url = new URL(`http://${req.headers['host']}${req.url}`);
-      const file = this.latestBuildFiles.files[url.pathname.slice(1)];
+      // Remove the leading slash from the URL path and convert to platform specific.
+      // The latest build files will use the platform path separator.
+      let pathname = url.pathname.slice(1);
+      if (isWindows) {
+        pathname = pathname.replaceAll(path.posix.sep, path.win32.sep);
+      }
+
+      const file = this.latestBuildFiles.files[pathname];
 
       if (file?.origin === 'disk') {
         this.serveFile(file.inputPath, undefined, res);