RFR: 8370691: Add new Float16Vector type and enable intrinsification of vector operations supported by auto-vectorizer [v8]

[Jatin Bhateja]

> Add a new  Float16lVector type and corresponding concrete vector classes, in addition to existing primitive vector types, maintaining operation parity with the FloatVector type.
> - Add necessary inline expander support.
>    - Enable intrinsification for a few vector operations, namely ADD/SUB/MUL/DIV/MAX/MIN/FMA.
> - Use existing Float16 vector IR and backend support.
> - Extended the existing VectorAPI JTREG test suite for the newly added Float16Vector operations.
>  
> The idea here is to first be at par with Float16 auto-vectorization support before intrinsifying new operations (conversions, reduction, etc).
> 
> The following are the performance numbers for some of the selected Float16Vector benchmarking kernels compared to equivalent auto-vectorized Float16OperationsBenchmark kernels.
> 
> <img width="1344" height="532" alt="image" src="https://github.com/user-attachments/assets/c8157c3c-22b0-4bc1-9de9-7a68cadb7b2a" />
> 
> Initial RFP[1] was floated on the panama-dev mailing list.
> 
> Kindly review the draft PR and share your feedback.
> 
> Best Regards,
> Jatin
> 
> [1] https://mail.openjdk.org/pipermail/panama-dev/2025-August/021100.html

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

  Including test changes from Bhavana Kilambi (ARM)

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28002/files
  - new: https://git.openjdk.org/jdk/pull/28002/files/44ac727d..7da5d147

Webrevs:
 - full: Webrev is not available because diff is too large
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28002&range=06-07

  Stats: 16 lines in 1 file changed: 10 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/28002.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28002/head:pull/28002

PR: https://git.openjdk.org/jdk/pull/28002