Japan’s Cabinet approved Friday a bill to regulate smartphone app stores to promote easier market access for third-party developers, in a move to challenge the duopoly exerted by industry giants Apple Inc. and Google LLC. The bill would require dominant smartphone operating system providers to allow the entry of third-party app stores and payment systems to increase competition. Under the new regulations, providers who fail to comply will be slapped with a penalty worth 20 percent of their domestic revenue related to the violation. The penalty can rise to 30 percent if the malpractice continue…