RFR: 8325064: C2 SuperWord: refactor construct_bb [v3]

[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 incrementally with one additional commit since the last revision:

  rename for Christian

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17657/files
  - new: https://git.openjdk.org/jdk/pull/17657/files/aaaaae63..9d0b575a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17657&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17657&range=01-02

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 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