Verify Currency against upstream OpenJDK8u121-b13.

This CL only performs reformatting/tweaks with no
behavior changes:

 - Add commented-out upstream code for most methods that were
   re-implemented on top of ICU; this makes it easier to
   review integration of upstream changes in future.

 - Add missing change summary to END markers.

 - Tweak change markers: s/use ICU/Use ICU./

 - Minor other tweaks to minimize diffs.

Test: Treehugger
Bug: 35910877

Change-Id: Icbe5cbd1d1fb03108b97377cac0dbb588c23f84c