src/vs/workbench/contrib/terminal/browser/terminalGroupService.ts/TerminalGroupService/instanceIsSplit
class TerminalGroupService:	instanceIsSplit(instance: ITerminalInstance): boolean {
		const group = this.getGroupForInstance(instance);
		if (!group) {
			return false;
		}
		return group.terminalInstances.length > 1;
	}