[vectorIntrinsics+mask] RFR: 8267368: Add masking support for reduction vector intrinsics [v3]

[Xiaohong Gong]

> This patch adds the masking support for vector reduction operations, including the Vector API java implementation and hotspot intrinsics changes. It adds the mask information to the reduction intrinsic method. With it:
>   - Both masked and non-masked reduction operations call the same hotspot intrinsics. The mask value and class are set to `"null"` for non-masked operations.
>   - Reduction IR with mask as another input will be generated if the platform supports the predicate feature for the op. Otherwise, the vector blend pattern will be generated like before.
> 
> Note that this patch only contains the Vector API java implementation and the hotspot intrinsics changes. No compiler mid-end and backend implementations are included.

Xiaohong Gong has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Use "VecMaskUsePred" to check whether predicate is supported
 - Merge panama-vector:vectorIntrinsics+mask into JDK-8267368
 - Merge panama-vector:vectorIntrinsics+mask into JDK-8267368
 - 8267368: Add masking support for reduction vector intrinsics

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Changes: https://git.openjdk.java.net/panama-vector/pull/86/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=86&range=02
  Stats: 684 lines in 42 files changed: 367 ins; 94 del; 223 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/86.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/86/head:pull/86

PR: https://git.openjdk.java.net/panama-vector/pull/86