[vectorIntrinsics] RFR: 8283709: Add x86 back-end implementation for bit BIT_COUNT operation [v7]

[Jatin Bhateja]

> Summary of changes:
> 
> - Patch re-uses existing C2 IR nodes and re-organizes LUT based JIT code sequence of VectorOperations.BIT_COUNT operation 
>   for sub-word type (BYTE, SHORT) vectors over X86 targets supporting AVA2 and AVX512 features.
> - Efficient single instruction POPCOUNT instruction is emitted for applicable targets. 
> 
> Kindly review and share you feedback.
> 
> Best Regards,
> Jatin

Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:

  8283709: Integer.bitCount((int)(byte_val) & 0xFF) is folded as LoadUB, this is auto-vectorized as load from Boolean vector. Adding missing types in macroassembler to cover these cases.

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Changes:
  - all: https://git.openjdk.java.net/panama-vector/pull/185/files
  - new: https://git.openjdk.java.net/panama-vector/pull/185/files/aab71a7a..05772da1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=185&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=185&range=05-06

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/185.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/185/head:pull/185

PR: https://git.openjdk.java.net/panama-vector/pull/185