chore(scripts): normalize paths and include typeRoots for Windows (#11933)

Short description of what this resolves:

Allows our e2e tests to run on a Windows machine

Changes proposed in this pull request:

Normalize paths using path.join()
Add typeRoots to the root tsconfig file
Change the spawnedCommand based on the OS
Fixes: #11551

scripts/demos/copy.config.js

@@ -4,7 +4,7 @@ var path = require('path');
 module.exports = {
   copyAssets: {
     src: [path.join(path.dirname(process.env.IONIC_APP_ENTRY_POINT), '..', 'assets', '**', '*')],
-    dest: '{{WWW}}/assets'
+    dest: path.join('{{WWW}}', 'assets')
   },
   copyIndexContent: {
     src: [path.join(process.cwd(), 'scripts', 'demos', 'index.html')],
@@ -12,7 +12,7 @@ module.exports = {
   },
   copyFonts: {
     src: [`${process.cwd()}/node_modules/ionicons/dist/fonts/**/*`, `${process.cwd()}/src/fonts/**/*`],
-    dest: '{{WWW}}/assets/fonts'
+    dest: path.join('{{WWW}}', 'assets', 'fonts')
   },
   copyPolyfills: {
     src: [path.join(process.cwd(), 'dist', 'demos', 'polyfills', 'polyfills.js')],