[vectorIntrinsics] RFR: 8283709: Add x86 back-end implementation for bit BIT_COUNT operation [v3]

[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: Adding new CPU feature AVX512_BITALG to JVMCI feature set.

-------------

Changes:
  - all: https://git.openjdk.java.net/panama-vector/pull/185/files
  - new: https://git.openjdk.java.net/panama-vector/pull/185/files/f2cd9cab..fce9fcbf

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=185&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=185&range=01-02

  Stats: 1 line in 1 file changed: 1 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