Google parent Alphabet unveiled a $70 billion share buyback and beat quarterly revenue estimates on Thursday, benefiting from steady growth in its digital advertising business, which helped offset muted growth at its cloud computing unit.Shares of the company jumped 6% in extended trading.President Trump’s trade policy has triggered worries of an economic downturn, prompting companies to rethink their spending on advertising. But analysts say the digital ad market still held its ground in the first quarter. ...