RFR: 8324775: C2 SuperWord: refactor visited sets [v3]

[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. This is necessary, unless we want to pass the visited set around into the recursive calls (I think not!)
> 
> 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`, and had to slightly adapt also its usages.

Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - manual merge because lines were too close
 - comment improvement by Vladimir
 - more removal
 - 8324775

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Changes: https://git.openjdk.org/jdk/pull/17594/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17594&range=02
  Stats: 129 lines in 2 files changed: 27 ins; 55 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