RFR: 8318458: Update javac and java manpages with restricted method options

[Maurizio Cimadamore]

This PR updates the man pages for `javac` and `java` to document:
* the new `javac` warning for restricted methods (`-Xlint:restricted`)
* the `java` option to allow access to restricted methods without warnings (`--enable-native-access`)

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jdk/pull/16249/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16249&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318458
  Stats: 21 lines in 2 files changed: 17 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/16249.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16249/head:pull/16249

PR: https://git.openjdk.org/jdk/pull/16249