TO MANY Americans, probably, the name Newfoundland has long stood for little except large black dogs and codfish. To strategists, however, the island's position at the crossroads of shipping in the North Atlantic has always given it special importance. And now the war, with the establishment of American bases on Newfoundland territory and the dramatic meeting between President Roosevelt and Prime Minister Churchill in Newfoundland waters, has brought it prominently into the consciousness of the wider public.