build(docs-infra): update docs examples `package.json` templates wrt `core-js` (#36143)

The `core-js` dependency is no longer included in `package.json` for
`cli`-type examples, but only for the `systemjs` ones. This commit
updates the `package.json` templates to reflect that (and also updates
the `npm-packages` guide accordingly).

PR Close #36143

aio/content/guide/npm-packages.md

@@ -93,9 +93,6 @@ features that Angular requires.
 The [Browser Support](guide/browser-support) guide explains which browsers need polyfills and
 how you can add them.
 
-The `package.json` for a new Angular workspace installs the [core-js](https://github.com/zloirock/core-js) package,
-which polyfills missing features for several popular browser.
-
 
 {@a dev-dependencies}
 

aio/tools/example-zipper/customizer/package-json/base.json

@@ -13,7 +13,6 @@
     "@angular/router",
     "@angular/upgrade",
     "angular-in-memory-web-api",
-    "core-js",
     "rxjs",
     "zone.js"
   ],

aio/tools/example-zipper/customizer/package-json/systemjs.json

@@ -25,6 +25,7 @@
     "@angular/platform-browser-dynamic",
     "@angular/router",
     "@angular/upgrade",
+    "core-js",
     "rxjs",
     "systemjs",
     "tslib",

aio/tools/examples/shared/boilerplate/systemjs/package.json

@@ -38,6 +38,7 @@
     "@angular/platform-browser-dynamic": "~9.0.3",
     "@angular/router": "~9.0.3",
     "@angular/upgrade": "~9.0.3",
+    "core-js": "^2.5.4",
     "rxjs": "~6.5.4",
     "tslib": "^1.10.0",
     "zone.js": "~0.10.3"