Drag and drop file to open

[dabbott]

The user should be able to drag and drop a .sketch file onto the canvas to open that file in Noya. This should replace the current document.

This should be similar to when we open a file via File > Open:

noya/packages/app/src/containers/Menubar.tsx

Line 60 in fa241b4

const handleOpen = useCallback(async () => {

We first need to decode the file, then dispatch setFile