TOKYO, March 31 (Reuters) - Japan has seen its share of the semiconductor market fall from 50% in the late 1980s to about 10% but still hosts some of the most advanced chipmaking equipment manufacturers, making it relevant to U.S. attempts to curb technology exports to China. The United States in October imposed restrictions on shipments of chipmaking tools to China to slow advances in its chip industry and ultimately its military, and has been seeking the cooperation of major chipmaking peers Netherlands and Japan. On Friday, Japan said it would restrict exports of 23 types of chipmaking gear, though...