Added user defined conversion operator in ConstBuffer for string_view.
Added user defined conversion operator in ConstBuffer for string_view.

davidbz/trafficserver,pbchou/trafficserver,pbchou/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,bryancall/trafficserver,davidbz/trafficserver,pbchou/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,pbchou/trafficserver,dyrock/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,vmamidi/trafficserver,dyrock/trafficserver,davidbz/trafficserver,duke8253/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,pbchou/trafficserver,dyrock/trafficserver,bryancall/trafficserver,davidbz/trafficserver,dyrock/trafficserver,bryancall/trafficserver,dyrock/trafficserver,pbchou/trafficserver,davidbz/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,dyrock/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,duke8253/trafficserver