feat(api-server): add endpoint to get shuffle state

[franz-dc]

Added API endpoint: /api/v1/shuffle (GET)

canSetFullscreen has been renamed to canUsePlayerControls to be used by other player control states other than fullscreen. Can be reverted back if that's not the desired outcome.

[ArjixWasTaken]

You should use ipc.handle and ipc.invoke instead of ipc.send() and ipc.once()

e.g.

- backend.ts
- renderer.ts

That way you won't care about race conditions, although in this particular case, a race condition should not be a big issue.

Edit: Actually, a race condition could cause an issue, your promise may never resolve when a race condition happens, now, I doubt that would happen, since it is a locally hosted API, but we should not take such risks.

Edit 2:
Oh I see, the renderer thread is what "handles" the request, that's why you did it this way.
So I assume electron doesn't support for the renderer to "handle" an event, because there can be multiple renderers!