RFR: 8307466: java.time.Instant calculation bug in until and between methods [v2]

[Roger Riggs]

> The implementation of java.time.Instant.until(I2, ChronoUnit) in some cases did not correctly borrow or carry from the nanos to the seconds when computing using ChronoUnit.MILLIS or ChronoUnit.MICROS.
> The errant computation was introduced by [JDK-8273369](https://bugs.openjdk.org/browse/JDK-8273369).

Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:

  Slight perf improvement using int instead of long for local nanosDiff

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13846/files
  - new: https://git.openjdk.org/jdk/pull/13846/files/8deb8df7..46d4918a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13846&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13846&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13846.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13846/head:pull/13846

PR: https://git.openjdk.org/jdk/pull/13846