RFR: 8372155: RealeaseInfoPlugin doesn't handle input file as UTF-8 properly

[Severin Gehwolf]

Please review this simple fix to `jlink`'s `--release-info` plugin to handle non-ASCII in vendor strings. The JDK build uses UTF-8 encoding for the produced `release` file that is being passed to `jlink` at build-time via the `--release-info` plugin. However, the plugin internally uses `java.util.Properties.load(InputStream)` API which assumes `ISO-8859-1` encoding of the input stream. The proposed fix is to use the `java.util.Prorperties.load(Reader)` API instead and pass it an `InputStreamReader` with `UTF-8` encoding.

Testing:
- [x] GHA
- [x] `test/jdk/tools/jlink` tests including the new reg-test which fails prior and passes after the fix.

Thoughts?

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Commit messages:
 - Add a test for the encoding issue
 - 8372155: RealeaseInfoPlugin doesn't handle input file as UTF-8 properly

Changes: https://git.openjdk.org/jdk/pull/28399/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28399&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372155
  Stats: 86 lines in 2 files changed: 84 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28399.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28399/head:pull/28399

PR: https://git.openjdk.org/jdk/pull/28399