SINGAPORE (Reuters) - Singapore state investor Temasek Holdings [TEM.UL] has joined the Facebook-backed Libra digital currency project which has faced intense scrutiny from global regulators worried its launch could erode national control over money.The entry of Temasek, which latest figures show has a portfolio value of just over S$300 billion ($210 billion), was announced by the Switzerland-based Libra Association, the entity managing the digital currency project, late Thursday. Temasek..