RFR: JDK-8316559: Refactor some util/Calendar tests to JUnit [v6]

[Justin Lu]

> Please review this PR which converts some tests under _Calendar_ to use JUnit. These tests either previously used the internal _IntlTest_, or used no framework at all. 
> 
> Any files named BugXXXXXXX.java will be renamed after review.

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

  Revert "rename files from bugXXXXXXX to something more descriptive"
  
  Renaming the files messes up the version history.
  
  This reverts commit a65b30987ba030c7698351b3afbc328b4eeb797b.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15853/files
  - new: https://git.openjdk.org/jdk/pull/15853/files/a65b3098..4e60ce55

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15853&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15853&range=04-05

  Stats: 18 lines in 9 files changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/15853.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15853/head:pull/15853

PR: https://git.openjdk.org/jdk/pull/15853