[vectorIntrinsics] RFR: x86 intrinsics for zero extension casts

[Mai Đặng Quân Anh]

This patch implements the zero extension intrinsics for x86. I also fix the bug with the previous implementation where the sign elimination mask is calculated incorrectly and add several tests for this operation. I hope this will be useful.

Thank you very much.

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Commit messages:
 - vector unsigned cast intrinsics

Changes: https://git.openjdk.java.net/panama-vector/pull/155/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=155&range=00
  Stats: 507 lines in 13 files changed: 486 ins; 0 del; 21 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/155.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/155/head:pull/155

PR: https://git.openjdk.java.net/panama-vector/pull/155