refactor(@schematics/angular): update new project rxjs version to ~7.4.0

`rxjs` 7 versions prior to 7.4.0 did not export the ES2015 variant in a way that could be leveraged via the new package.json `exports` feature. As a result, prior versions would cause larger ES5 variants of rxjs to be bundled within applications. Version 7.4.0 is now set as the minimum version for new projects to allow for the ES2015 rxjs code to be used when building applications.

Author: clydin

packages/schematics/angular/utility/latest-versions/package.json

@@ -12,7 +12,7 @@
     "karma-jasmine": "~4.0.0",
     "karma": "~6.3.0",
     "ng-packagr": "~13.0.0-next.0",
-    "rxjs": "~7.3.0",
+    "rxjs": "~7.4.0",
     "tslib": "^2.3.0",
     "typescript": "~4.4.3",
     "zone.js": "~0.11.4"