RFR: 8278171: [vectorapi] Mask incorrectly computed for zero extending cast

[Mai Đặng Quân Anh]

This patch implements vector unsigned upcast intrinsics for x86. I also fixed a bug in the current implementation where the zero extension masks are computed incorrectly and add relevant tests.

Thank you very much.

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Commit messages:
 - revert intrinsics
 - Merge branch 'master' into vectorUnsignedCastIntrinsics
 - retain relevant changes

Changes: https://git.openjdk.java.net/jdk/pull/6634/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6634&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278171
  Stats: 322 lines in 2 files changed: 321 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6634.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6634/head:pull/6634

PR: https://git.openjdk.java.net/jdk/pull/6634