SWF Editor - Add API to set SWF theme and refresh the Canvas

Implement and expose an js API to set  "dark" or "light" theme on the SWF Canvas and refresh the canvas to apply the style changes.

The theme should be changed by calling the javascript function "applyTheme('[light/dark])"  exposed in the editorFrame similar to the way the functions "set/getContent()" are called.   

How to test:

• From the console tab select the Active Frame(VsCode) / editorFrame(Browser)
• Similar to the set/getContent functions call the applyTheme("[dark/light]")
  • e.g.
    • await gwtEditorBeans.get("SWDiagramEditor").get().applyTheme("dark")
    • await gwtEditorBeans.get("SWDiagramEditor").get().applyTheme("light")

Expected Behavior:

• By calling applyTheme() function it must be possible to switch in between light and dark themes.
• Theme changes on loaded diagram will cause the diagram to reload.
• The theme should remain the same if the diagram is modified from text editor.