By Laura Sanicola (Reuters) -Refiners worldwide are struggling to meet global demand for diesel and gasoline, exacerbating high prices and aggravating shortages from big consumers like the United States and Brazil to smaller countries like war-ravaged Ukraine and Sri Lanka. World fuel demand has rebounded to pre-pandemic levels, but the combination of pandemic closures, sanctions on Russia and export quotas in China are straining refiners’ ability to meet demand. China and Russia are two of the three biggest refining countries, after the United States. All three are below peak processing level…