fix(@angular/build): allow component HMR with a service worker

When the service worker option is enabled, each code update will cause
the `ngsw.json` configuration file to change due to the different hashes
of the updated output. This is problematic for component HMR usage with
the development server since the full reload fallback logic would be triggered
due to the changed `ngsw.json` file.  To avoid this problem, the `ngsw.json`
configuration file is now special cased within the fallback logic.

Author: clydin

packages/angular/build/src/builders/application/build-action.ts

@@ -327,8 +327,9 @@ function* emitOutputResults(
     if (needFile) {
       if (file.path.endsWith('.css')) {
         hasCssUpdates = true;
-      } else if (!/(?:\.m?js|\.map)$/.test(file.path)) {
+      } else if (!/(?:\.m?js|\.map)$/.test(file.path) && file.path !== 'ngsw.json') {
         // Updates to non-JS files must signal an update with the dev server
+        // except the service worker configuration which is special cased.
         incrementalResult.background = false;
       }