WASHINGTON — The world’s major central banks launched a joint action to provide cheap, emergency U.S. dollar loans to banks in Europe and elsewhere, a sign of growing alarm among policy makers about stresses in Europe and in the global financial system. The Fed, ECB and other central banks took coordinated action to support the global financial system as Europe’s rolling debt crisis continues to trouble markets. The coordinated action doesn’t directly address Europe’s government-debt and budget woes. Instead, it is aimed at alleviating the impact of those troubles on global markets. Moreover, it raises the prospect of other steps by central bankers to prevent a repeat of the 2008 financial crisis.