src/vs/workbench/contrib/terminal/browser/terminalGroupService.ts/TerminalGroupService/activeGroup
class TerminalGroupService:	set activeGroup(value: ITerminalGroup | undefined) {
		if (value === undefined) {
			this.activeGroupIndex = -1;
			return;
		}
		this.activeGroupIndex = this.groups.findIndex(e => e === value);
	}