RFR: 8301752: [IR Framework] Add more IR framework examples

[Christian Hagedorn]

This patch adds some more examples to the already existing IR framework usage examples. I also improved some comments.

Thanks,
Christian

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Commit messages:
 - 8301752: [IR Framework] Add more IR framework examples

Changes: https://git.openjdk.org/jdk/pull/12406/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12406&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301752
  Stats: 77 lines in 3 files changed: 70 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/12406.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12406/head:pull/12406

PR: https://git.openjdk.org/jdk/pull/12406