RFR: 8210336: DateTimeFormatter predefined formatters should support short time zone offsets [v2]

[Naoto Sato]

> This PR is a follow-on fix to [JDK-8032051](https://bugs.openjdk.org/browse/JDK-8032051), where it allowed short offsets only for ZonedDateTime parsing. This fix allows all predefined ISO formatters to accept short offsets. A corresponding CSR has been drafted.

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

  Added a test that asserts parse with hour-only offset

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29393/files
  - new: https://git.openjdk.org/jdk/pull/29393/files/14c4beb1..1b253613

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29393&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29393&range=00-01

  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29393.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29393/head:pull/29393

PR: https://git.openjdk.org/jdk/pull/29393