RFR: 8324775: C2 SuperWord: refactor visited sets

[Emanuel Peter]

Subtask of https://github.com/openjdk/jdk/pull/16620

Currently, the visited set is a "global" set that is reused all through SuperWord:
`_visited`, `_post_visited`, and also `_stk`.

This makes other refactorings difficult. I am refactoring all related code to make the visited sets local, with use of ResourceMark.

I am also refactoring the `independent` queries: from using recursive function calls to iterative.

At the same time, I wanted the code of `find_dependence` to become easier, and closer to `independent`, hence I re-defined it to `mutually_independent`.

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Commit messages:
 - more removal
 - 8324775

Changes: https://git.openjdk.org/jdk/pull/17594/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17594&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324775
  Stats: 128 lines in 2 files changed: 27 ins; 54 del; 47 mod
  Patch: https://git.openjdk.org/jdk/pull/17594.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17594/head:pull/17594

PR: https://git.openjdk.org/jdk/pull/17594