Add event listener for resize events

[ibdafna]

This PR adds an event listener so that lumino based widgets rendered in a classic notebook can receive a resize message when a window resize event triggers.

[jasongrout]

Fixes #2467

[jasongrout]

@ibdafna, thanks for looking into this.

I think we should register the handler in the classic notebook widget manager once, then when it is triggered, have the classic notebook manager go through each of the top-level widgets and trigger the lumino event. And probably do the same for the html manager.

The way things are set up right now in this PR, it looks like every widget will register a handler with window (whether it needs to or not).

@ibdafna - I'm happy to connect over video to walk through this if you want.

[ibdafna]

@ibdafna, thanks for looking into this.

I think we should register the handler in the classic notebook widget manager once, then when it is triggered, have the classic notebook manager go through each of the top-level widgets and trigger the lumino event. And probably do the same for the html manager.

The way things are set up right now in this PR, it looks like every widget will register a handler with window (whether it needs to or not).

@ibdafna - I'm happy to connect over video to walk through this if you want.

Thank you - yes, I'll reach out!

[jasongrout]

Thanks! I found a few things while testing, noted below.

[jasongrout]

FYI, I rebased on master

[jasongrout]

@ibdafna - I rebased and fixed a few issues with the examples, and checked manually that the resize event is now happening for the classic notebook and the html manager. Thanks again!