RFR: 8357649: IGV: add block index to the supplemental node properties

Fri May 23 13:47:02 UTC 2025

This PR adds the block index to IGV node properties as soon as the CFG has been scheduled. This is really handy when working on peepholes, where one has to work with block indices.

![Screenshot from 2025-05-23 15-35-29](https://github.com/user-attachments/assets/1a895e07-cf5f-4eed-afd0-08fe26cf0266)

Testing:
 - [ ] [Github Actions](https://github.com/mhaessig/jdk/actions?query=branch%3AJDK-8357649-block-index)
 - [ ] tier1, tier2, and some Oracle internal testing on Oracle supported platfors and OSs

Shout out to @robcasloz for coming up with an initial version of this patch.

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Commit messages:
 - Add block_index to IGV nodes

Changes: https://git.openjdk.org/jdk/pull/25414/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25414&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357649
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25414.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25414/head:pull/25414

PR: https://git.openjdk.org/jdk/pull/25414