Playground: Upgrade BJS and add glTF serializer

[alexchuber]

This PR adds a quick test for the glTF serializer in the Playground, updating BJS along the way.

• Upgrade BJS to latest
• Fix win32 install test failure
• Add the Blob polyfill, NativeEncoding plugin, and babylonjs-serializers package throughout the Playground app
• Port a visualization test from BJS for the glTF serializer
  • Note: I would port over more, but all the rest happen to use the File API, which is not yet supported in Native.

[alexchuber]

I'm not actually sure this will fix the win32 install test failure, but it seemed to be an obvious difference. Will test.

[alexchuber]

I think the test is failing because we're expecting the old Blob polyfill in this function
which is being called in this line