By Simon Jessop LONDON (Reuters) – World stocks headed for their worst week since markets’ pandemic meltdown in March 2020 as leading central banks doubled down on tighter policy in an effort to tame inflation, setting investors on edge about future economic growth. The biggest U.S. rate rise since 1994, the first such Swiss move in 15 years, a fifth rise in British rates since December and a move by the European Central Bank to bolster the indebted south ahead of future rises all took turns in roiling markets. The Bank of Japan was the only outlier in a week where money prices rose around the…