src/vs/workbench/contrib/terminal/browser/terminalGroupService.ts/TerminalGroupService/activeGroup
class TerminalGroupService:	get activeGroup(): ITerminalGroup | undefined {
		if (this.activeGroupIndex < 0 || this.activeGroupIndex >= this.groups.length) {
			return undefined;
		}
		return this.groups[this.activeGroupIndex];
	}