Fix broadcast service debt

[jrieken]

While working on #70319 I have moved the IBroadcastService-service definition to common. However, there is only an implementation for electron-node (not electron-node-less).

Looking at the service and it's usages it seems like a kitchen-sink service that should be avoidedby using "topic"-services, like a service that manages debug output or one that's about windows and themes.

[isidorn]

I am fine with dismantling it into smaller services and introducing one only for the debug use case

fyi @bpasero

[bpasero]

Yeah a good idea 👍

[weinand]

I've created #70835 for the debug case.

[bpasero]

Leaving vscode:changeColorTheme (from parts splash) for @aeschli

[isidorn]

I have moved the debug stuff as covered by this item #70835
@aeschli if you like my changes from there I can do the same for your vscode:changeColorTheme and we fully get rid of the broadcastService.