RFR: JMC-7258: Use the public XLST classes for the release notes

[Patrick Reinhart]

Signed-off-by: Patrick Reinhart <patrick at reini.net>

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Commit messages:
 - JMC-7258: Use the public XLST classes for the release notes

Changes: https://git.openjdk.java.net/jmc/pull/252/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=252&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7258
  Stats: 77 lines in 1 file changed: 75 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jmc/pull/252.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/252/head:pull/252

PR: https://git.openjdk.java.net/jmc/pull/252