[lworld+vector] RFR: JDK 8327435: [lworld+vector] Align existing Vector API support with JEP 401

[Jatin Bhateja]

-  Align existing vector API java side implementation with JEP 401[1] and future JEP Null-Restricted Value Class Types[2]
-  Existing primitive value class based vector payloads becomes value classes decorated with LosselyConsistent and ImplicitlyConstructible annotations, this
   relaxes atomicity constraints on instance updates and guarantees initialization by a default value.
-  Payload field in concrete values classes is NullRestricted to promote its flattening.
-  In future we can consider making publicly exposed abstract vector classes as sealed classes to restrict its sub-classing by known concrete vector classes.

All existing Vector API JTREG tests are passing at various AVX level with/wo -XX:+DeoptimizeALot.

Best Regards,
Jatin
[1] https://openjdk.org/jeps/401
[2] https://openjdk.org/jeps/8316779

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Commit messages:
 - JDK-8327435: [lworld+vector] Align existing Vector API support with JEP 401

Changes: https://git.openjdk.org/valhalla/pull/1034/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1034&range=00
  Stats: 316 lines in 40 files changed: 234 ins; 22 del; 60 mod
  Patch: https://git.openjdk.org/valhalla/pull/1034.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1034/head:pull/1034

PR: https://git.openjdk.org/valhalla/pull/1034