<i18n dev> RFR: 8340554: Improve MessageFormat readObject checks [v2]

[Justin Lu]

> Please review this PR which improves the readObject logic for _j.text.MessageFormat_.
> 
> No offset should be larger than the pattern length. We already ensure the offsets when consumed backwards are equal/descending. The existing first/initial check was off by 1 since it was checking against the pattern length + 1; (see L2040 and L2043).
> 
> Please see the JBS issue for further info and other test details.

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

  review: clarify test comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21570/files
  - new: https://git.openjdk.org/jdk/pull/21570/files/dc3e952e..3730d628

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21570&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21570&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21570.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21570/head:pull/21570

PR: https://git.openjdk.org/jdk/pull/21570