ESM Script docs

[marklundin]

We need to add relevant documentation for using ESM Script as features rolls out. A non-exhaustative list;

• General Class based syntax
• Attributes Definitions
• import /exporting including path mapping
• Caveats/Limitations
  • Dynamic Import Expressions
  • Attribute Getters/Setters
• Bundling
• ESM Examples - Update examples/tutorials with pc.createScript syntax to show ESM equivalent. This can be shown as a docusaurus Tab, with some persistent state that applies site wide. Add ESM Script Documentation #644

[marklundin]

This has been completed here https://github.com/playcanvas/developer.playcanvas.com/tree/esm-script-examples. Awaiting approval