Only show available image sizes in block editor / post editing context

[roborourke]

The cropping UI shows all registered image sizes but in order to maintain compatibility with the image block only image sizes with a label (added via a filter) that the editor is aware of can be inserted into the editor.

Because the size selected in the modal that is being cropped is the size inserted (if allowed) it is confusing when trying to insert a crop or size that is not supported in the editor.

The UI should only show the image sizes that can be inserted the editor when the modal has been opened from an image block or similar.