Add details for event dispatching and forking process

[majido]

Section 3 of the spec discusses the fork and dispatch semantic but it is very sparse. We should add the following:

• Order of dispatch, is there any ordering gauranteed? e.g., do we call handlers in worker in a specific order? what about handlers in main in relationship to worker handlers.

• Details of event dispatch e.g., what happens if one handler (main or worklet) prevents event propagation or default action?

• Details of stripping DOM