src/vs/workbench/contrib/terminal/browser/terminalGroupService.ts/TerminalGroupService/_getIndexFromId
class TerminalGroupService:	private _getIndexFromId(terminalId: number): number {
		let terminalIndex = this.instances.findIndex(e => e.instanceId === terminalId);
		if (terminalIndex === -1) {
			throw new Error(`Terminal with ID ${terminalId} does not exist (has it already been disposed?)`);
		}
		return terminalIndex;
	}