[vectorIntrinsics] RFR: Improve mask reduction operations on AVX

[Mai Đặng Quân Anh]

Hi,
This patch improves the logic of vector mask reduction operations on AVX, especially int, float, long, double, by using vmovmskpd and vmovmskps instructions. I also do a little refactoring to reduce duplication in toLong. The patch temporarily disables these operations on Neon, though.
Thank you very much.

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Commit messages:
 - missing assert
 - improve mask reduction operations

Changes: https://git.openjdk.java.net/panama-vector/pull/158/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=158&range=00
  Stats: 99 lines in 8 files changed: 52 ins; 22 del; 25 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/158.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/158/head:pull/158

PR: https://git.openjdk.java.net/panama-vector/pull/158