[vectorIntrinsics+compress] RFR: 8275231: Intrinsify VectorMask.compress API for X86 target.

[Jatin Bhateja]

Summary of changes:
- Inline expansion of VectorMask.compress API.
- X86 backend support for both AVX-512 and legacy targets.

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Commit messages:
 - 8275231: Intrinsify VectorMask.compress API for X86 target.

Changes: https://git.openjdk.java.net/panama-vector/pull/156/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=156&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275231
  Stats: 547 lines in 55 files changed: 469 ins; 6 del; 72 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/156.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/156/head:pull/156

PR: https://git.openjdk.java.net/panama-vector/pull/156