RFR: 8370691: Add new Float16Vector type and enable intrinsification of vector operations supported by auto-vectorizer [v3]

[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="1449" height="629" alt="image" src="https://github.com/user-attachments/assets/b4474361-9886-4315-a614-f4073fd075b9" />
> 
> 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 with a new target base due to a merge or a rebase. The pull request now contains 15 commits:

 - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
 - Cleanups
 - Adding support for custom basic  type T_FLOAT16, passing BasicType lane types to inline expander entries
 - Cleaning up interface as per review suggestions
 - Some cleanups
 - Fix some JTREG failures
 - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
 - Revamped JTreg test generation and bug fixes
 - Cleanups
 - Removing redundant warmup constraint
 - ... and 5 more: https://git.openjdk.org/jdk/compare/8bafc2f0...f34d324f

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Changes: https://git.openjdk.org/jdk/pull/28002/files
  Webrev: Webrev is not available because diff is too large
  Stats: 509516 lines in 232 files changed: 281237 ins; 226539 del; 1740 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