RFR: 8331646: Add specific regression leap year tests [v4]

[serhiysachkov]

> Calendar.add() tests that describe its behavior.

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

  JDK-8331646 updating impl according to review requests

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19082/files
  - new: https://git.openjdk.org/jdk/pull/19082/files/4bb425da..f6ba2e31

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19082&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19082&range=02-03

  Stats: 32 lines in 1 file changed: 11 ins; 3 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/19082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19082/head:pull/19082

PR: https://git.openjdk.org/jdk/pull/19082