SYDNEY (Reuters) -Top Australian supermarket chain Woolworths said shelf prices had fallen in the March quarter as it competed for customers facing persistently high living costs, offsetting a consumer backlash but frustrating investors who sent shares lower. The quarterly update on Thursday shows the narrow path for Woolworths and No.2 rival Coles, which dominate Australian grocery sales. For Woolworths, which gets nearly 40 cents of every dollar spent by Australians in a supermarket, that meant cutting prices of fruit, vegetables and meat, which dragged down average prices by 0.2% in the 1...