src/vs/workbench/contrib/terminal/browser/terminalEditorService.ts/TerminalEditorService/splitInstance
class TerminalEditorService:	splitInstance(instanceToSplit: ITerminalInstance, shellLaunchConfig: IShellLaunchConfig = {}): ITerminalInstance {
		const input = this.getOrCreateEditorInput(instanceToSplit);
		const instance = this._terminalInstanceService.createInstance(shellLaunchConfig, TerminalLocation.Editor);
		input.setCopyInstance(instance);
		this._commandService.executeCommand('workbench.action.splitEditor');
		return instance;
	}