[vectorIntrinsics] RFR: 8305461: [vectorapi] Add VectorMask::xor, rename VectorMask::eq to VectorMask::xorNot

[Quan Anh Mai]

Hi,

This patch adds `VectorMask::xor` to the public API, as well as renames `VectorMask::eq` to `VectorMask::xorNot` for consistency with other logical operations. I also add unit tests for all logical vector operations to `test/jdk/jdk/incubator/vector`. Please kindly review and give your opinions on this change.

Thanks a lot.

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Commit messages:
 - tests
 - remove dangling docs
 - add final
 - maskxor

Changes: https://git.openjdk.org/panama-vector/pull/212/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-vector&pr=212&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305461
  Stats: 2855 lines in 64 files changed: 2408 ins; 283 del; 164 mod
  Patch: https://git.openjdk.org/panama-vector/pull/212.diff
  Fetch: git fetch https://git.openjdk.org/panama-vector.git pull/212/head:pull/212

PR: https://git.openjdk.org/panama-vector/pull/212