RFR: 8329273: C2 SuperWord: Some basic MemorySegment IR tests [v2]

[Emanuel Peter]

> I could not find any IR vectorization tests for `MemorySegment` yet.
> 
> I make sure to exercise different backing types:
> - arrays
> - buffers
> - native memory
> 
> I filed a follow-up RFE, to eventually make all cases where I have "FAILS" vectorize:
> 
> [JDK-8331659](https://bugs.openjdk.org/browse/JDK-8331659): C2 SuperWord: investicate failed vectorization in compiler/loopopts/superword/TestMemorySegment.java

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 25 additional commits since the last revision:

 - Merge branch 'master' into JDK-8329273-memory-segment-ir-tests
 - fix tabs
 - speed up test
 - small cosmetic fix
 - make things static
 - long loop tests
 - handle AlignVector
 - int cases
 - int-index case
 - disable mixed tests
 - ... and 15 more: https://git.openjdk.org/jdk/compare/43da3db1...6f760dfd

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18535/files
  - new: https://git.openjdk.org/jdk/pull/18535/files/b6f16a58..6f760dfd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18535&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18535&range=00-01

  Stats: 43101 lines in 1987 files changed: 18450 ins; 16140 del; 8511 mod
  Patch: https://git.openjdk.org/jdk/pull/18535.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18535/head:pull/18535

PR: https://git.openjdk.org/jdk/pull/18535