RFR: 8325064: C2 SuperWord: refactor construct_bb [v2]

[Emanuel Peter]

> Subtask of https://github.com/openjdk/jdk/pull/16620
> 
> The goal is to further disentangle different "components" in Superword.
> 
> In this refactoring, I disentangle the `bb`, `reduction` and `memory_slice` "components" which were all intertwined in `construct_bb`.
> 
> 1. Move memory slice code -> `analyze_memory_slices`.
> 2. Remove reduction checking code -> simply use the `is_marked_reduction_loop` condition outside.
> 3. `_data_entry`: was used for non-CFG nodes in the loop that have no input node that is also inside the loop. But that actually never happens! I removed that array, and replaced the code with verification.

Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into JDK-8325064
 - Merge branch 'master' into JDK-8325064
 - small improvements
 - 8325064

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/17657/files
  - new: https://git.openjdk.org/jdk/pull/17657/files/8961b77a..aaaaae63

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17657&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17657&range=00-01

  Stats: 9152 lines in 260 files changed: 6006 ins; 1521 del; 1625 mod
  Patch: https://git.openjdk.org/jdk/pull/17657.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17657/head:pull/17657

PR: https://git.openjdk.org/jdk/pull/17657