RFR: 8329273: C2 SuperWord: Some basic MemorySegment IR tests [v3]

[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 incrementally with one additional commit since the last revision:

  Apply suggestions from code review
  
  Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18535/files
  - new: https://git.openjdk.org/jdk/pull/18535/files/6f760dfd..3cbb4664

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18535&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18535&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 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