perf(@ngtools/webpack): rebuild Angular required files asynchronously

This change adjusts the Angular required files rebuilding logic to not block on each individual file's Webpack module rebuild. Now all required Webpack modules are discovered then rebuilt asynchrounously and only blocked on the full list of rebuilds. The promise-based Webpack rebuild function is also now only created if a rebuild is required.

(cherry picked from commit f62b042)

Author: clydin

packages/ngtools/webpack/src/ivy/plugin.ts

@@ -331,9 +331,6 @@ export class AngularWebpackPlugin {
       return;
     }
 
-    const rebuild = (webpackModule: Module) =>
-      new Promise<void>((resolve) => compilation.rebuildModule(webpackModule, () => resolve()));
-
     const filesToRebuild = new Set<string>();
     for (const requiredFile of this.requiredFilesToEmit) {
       const history = this.fileEmitHistory.get(requiredFile);
@@ -356,12 +353,17 @@ export class AngularWebpackPlugin {
     }
 
     if (filesToRebuild.size > 0) {
-      for (const webpackModule of [...modules]) {
+      const rebuild = (webpackModule: Module) =>
+        new Promise<void>((resolve) => compilation.rebuildModule(webpackModule, () => resolve()));
+
+      const modulesToRebuild = [];
+      for (const webpackModule of modules) {
         const resource = (webpackModule as NormalModule).resource;
         if (resource && filesToRebuild.has(normalizePath(resource))) {
-          await rebuild(webpackModule);
+          modulesToRebuild.push(webpackModule);
         }
       }
+      await Promise.all(modulesToRebuild.map((webpackModule) => rebuild(webpackModule)));
     }
 
     this.requiredFilesToEmit.clear();