RFR: 8351414: C2: MergeStores must happen after RangeCheck smearing

[Emanuel Peter]

With [JDK-8348959](https://bugs.openjdk.org/browse/JDK-8348959) we see that there can be some issues when RangeCheck smearing happens in the same IGVN phase as MergeStores. It means that some RangeChecks are still around as we do MergeStores, and then we cannot merge as many stores as we would like. We should ensure that RangeCheck smearing happens during post-loop-opts, and then MergeStores happens in a separate dedicated IGVN round afterwards.

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Commit messages:
 - actually do igvn and add print_method
 - clear flag after clone
 - more fix, and more comments
 - JDK-8351414

Changes: https://git.openjdk.org/jdk/pull/23944/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23944&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351414
  Stats: 107 lines in 8 files changed: 103 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/23944.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23944/head:pull/23944

PR: https://git.openjdk.org/jdk/pull/23944