Update java.util.Formatter to 8u60.

The main change is that it now supports formatting of java.time types.

- Adapt relevant test to Android sepcifics.
- Add Android-changed comments where appropriate
- Removed unused mantissa() and exponent() methods

Bug: 28832222
Test: run cts -m CtsLibcoreOjTestCases
Change-Id: I8a5de3f4bd39b6bad09850d4e5329a54331a2315