src/vs/workbench/contrib/terminal/browser/terminalEditorService.ts/TerminalEditorService/activeInstance
class TerminalEditorService:	get activeInstance(): ITerminalInstance | undefined {
		if (this.instances.length === 0 || this._activeInstanceIndex === -1) {
			return undefined;
		}
		return this.instances[this._activeInstanceIndex];
	}