RFR: 8297879: javadoc link to preview JEP 1000 has grouping character comma

[Pavel Rappo]

Please review this simple bugfix to properly construct links to preview JEPs.

The most straightforward fix I could think of was to pass `String` rather than `int` (`Integer`) to a method, which eventually calls `java.text.MessageFormat.format(String, Object...)`.

For the test, I decided to be ~lazy~ practical and piggyback on the existing infrastructure. The alternatives were:

 1. slap `noreg-hard` on the JBS bug and skip testing
 2. create a sophisticated test that dynamically adds a constant into the `PreviewFeature.Feature` enum, annotates some class with `PreviewFeature` with that constant, and finally documents that class with `PreviewFeature` patched into `java.base`

While (1) is insufficient, (2) seems overkill in this case.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/18350/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18350&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297879
  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18350.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18350/head:pull/18350

PR: https://git.openjdk.org/jdk/pull/18350