Run jetifier against prebuilts directly rather than classes.jar

It turns out that the resource files inside the .aar files may
need rewriting too

Bug: 72552006
Test: Set LOCAL_JETIFIED_ENABLED for a prebuilt and built it
      See also one of the patches after this one and its topic
      which contains a sample for testing
Change-Id: I89d0b4aa8d5c6ae3abc2344dd05222cf9672d5c0