(Bloomberg) -- Across much of the developed world, one of the most dependable drivers of economic growth is faltering.Most Read from BloombergTruce Talks Shift to Qatar as Hamas Hits Israel Border CrossingFrance’s Macron Calls for Reset of Economic Ties With ChinaBuffett Praises Apple After Trimming It, Drops Paramount StakeEverything Apple Plans to Show at May 7 ‘Let Loose’ iPad EventWorsening Weather Is Igniting a $25 Billion MarketFor decades, the rapid inflow of migrants helped countries inc