Make diagram resize configurable

[NiklasRentzCAU]

I am talking specifically about this line:
https://github.com/eclipse/sprotty-theia/blob/e14752e73bd553881891355a44d3dc6173ea9228/src/theia/diagram-widget.ts#L142

Currently on resize the zoom level is always reset with the CenterAction that is forced to be executed here. I would like to have this configurable so that a FitToScreenAction or no action at all is executed instead of the CenterAction.

[JanKoehnlein]

Why not just override DiagramWidget#onResize in your own subclass?

[NiklasRentzCAU]

I also had that option in mind, but I think the configurability on the Sprotty side leads to better maintainability on projects that want different behavior, such as our project.

Overriding this method would require to also reimplement the other functionality in the method - reading the bounds from the internal node property, initializing the canvas with that and calling the super method. While overriding the method, the super.super implementation can obviously not be called, so the concept of inheritance gets broken in this method, if I just do not want to call the center action, but keep all other functionality the same.

One thing I just noticed is that the super call actually does not do anything, so yes, just overriding is possible without breaking the code, but I think my point is still valid. Why does the onResize function even call the super implementation, if it is a no-op?

[JanKoehnlein]

PRs are welcome

[spoenemann]

I removed the center action in #63. I'll put it into a separate method to make it better configurable.