[jdk19] RFR: 8291512: Snippetize modules API examples

[Mark Reinhold]

The specification of the modules API contains several non-normative code examples. We should convert them to use snippets, per [JEP 413](https://openjdk.org/jeps/413).

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Commit messages:
 - 8291512: Snippetize modules API examples

Changes: https://git.openjdk.org/jdk19/pull/156/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19&pr=156&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291512
  Stats: 22 lines in 4 files changed: 2 ins; 9 del; 11 mod
  Patch: https://git.openjdk.org/jdk19/pull/156.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/156/head:pull/156

PR: https://git.openjdk.org/jdk19/pull/156