Add dark mode theme support to SWF editor in order to match VsCode and Backstage look & feel.

It should be possible to switch between light and dark mode by calling a function exposed through the js interface of the editor. So if the theme changes from outside it should be possible to propagate the change to SWF editor.

Expected behavior:

• In vscode, if the theme is set or changed to dark it should be applied to SWF editor as well, otherwise the light theme should be set.
• For other channels the theme change shall be done by calling a js function to set the theme.