RFR: 8303440: The "ZonedDateTime.parse" may not accept the "UTC+XX" zone id [v2]

[Naoto Sato]

> This change is to fix a regression caused by the fix to [JDK-8234347](https://bugs.openjdk.org/browse/JDK-8234347). The previous fix was simply disabling offset-based parsing if the parser was text-based. Instead, check if it is an offset or not by explicitly comparing the character with '+'/'-' and continue offset parsing if it is.

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

  now() -> of() to avoid DST

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12868/files
  - new: https://git.openjdk.org/jdk/pull/12868/files/966b8f67..5cda8482

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12868&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12868&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12868.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12868/head:pull/12868

PR: https://git.openjdk.org/jdk/pull/12868