Android patch: Patch 11.0.13-ga java.time implementation and tests

Implementation patches:
1. SystemClock.instant() reverts to the existing implementation
   until we implement nanosecond-level resolution of the clock
2. DateTimeFormatter.localizedBy is re-implemented by using ICU.
3. LocalDate.getEra() returns a backward-compatible type

Javadoc changes
4. Trivial javadoc fix in DateTimeFormatterBuilder. It's a upstream bug.
5. Hide localizedBy() in javadoc until we expose the API later.

Test patches: See inline comments

Bug: 180577079
Test: CtsLibcoreTestCases
Test: CtsLibcoreOjTestCases
Change-Id: I240273ff55ea6e6da7abf0b0c8c0d02e01700e69
14 files changed