Start moving window/document to use layout service

[Tyriar]

Fixes #195804

[Tyriar]

@bpasero am I on the right track here?

Is it correct to be using this._layoutService.container.ownerDocument to get the primary document? I end up doing this a lot, do we have a layout service API for fetching the primary window and it's document directly? Something like this:

export interface ILayoutService {
  readonly primaryContainer: HTMLElement; // name would make this clearer
  readonly primaryDocument: Document;
  readonly primaryWindow: Window;
}

[bpasero]

@Tyriar this looks good, except for document.createElement: you should use the global main document for now. The ownerDocument will automatically change as soon as the element is appended into the floating window. The advantage of document.createElement is that things like instanceof HTMLElement continue to work.

As for the additional properties on the layout service: I am really not sure that is a good idea because:

• the main window and document are always accessible as a global
• the correct window and document should always be computed based on the parent HTMLElement that you get to create your elements in and not by going to a service

done