RFR: 2279: Improve JSONNumber::asInt usage to prevent future break

[Zhao Song]

[SKARA-2277](https://bugs.openjdk.org/browse/SKARA-2277) is an instance of a breakage caused by improper usage of JSONNumber::asInt. In our project, there are other usages of JSONNumber::asInt, we should clean them up to prevent future break.

As Erik said, he thinks it's fine to treat user ids and repository ids as int.

Here are the other 2 places that might break.

GitLabRepository::toCommitComment treats note ids as int.
GitHubPullRequest::reviews treats review ids as int.

Besides, I changed the type of id from int to String in Review.java

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Commit messages:
 - update
 - SKARA-2279

Changes: https://git.openjdk.org/skara/pull/1657/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1657&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2279
  Stats: 25 lines in 6 files changed: 0 ins; 0 del; 25 mod
  Patch: https://git.openjdk.org/skara/pull/1657.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1657/head:pull/1657

PR: https://git.openjdk.org/skara/pull/1657