RFR: 2307: PullRequestCheckIssueVisitor generates only one error message per Issue type [v2]

[Zhao Song]

> When testing [SKARA-2303](https://bugs.openjdk.org/browse/SKARA-2303), I found that even when there are few binary files in a diff, the pr body only warns about one binary file. Then I found that in PullRequestCheckIssueVisitor, we are using HashMap<Check, String> to store the error messages, so if there are few issues with the same type, the HashMap is only able to save the last error message.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  set limit for error messages

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Changes:
  - all: https://git.openjdk.org/skara/pull/1662/files
  - new: https://git.openjdk.org/skara/pull/1662/files/c50dc783..53fd8a14

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1662&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1662&range=00-01

  Stats: 10 lines in 1 file changed: 6 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1662.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1662/head:pull/1662

PR: https://git.openjdk.org/skara/pull/1662