RFR: 8355585: Aarch64: Add aarch64 backend for Float16 vector operations [v4]

[Bhavana Kilambi]

> This patch adds aarch64 backend (both Neon and SVE) for FP16 vector operations - add, mul, sub, div, min, max, sqrt and fma.
> 
> Testing:
> JTREG tests - hotspot_all, jdk (tier 1-3) and langtools (tier 1) pass on aarch64 which also includes the JTREG test to test the FP16 vector operations - `test/hotspot/jtreg/compiler/vectorization/TestFloat16VectorOperations.java`

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

 - Merge master
 - Remove additional spaces in the aarch64_vector_ad.m4 file
 - Address review comments
 - 8355585: Aarch64: Add aarch64 backend for Float16 vector operations
   
   This patch adds aarch64 backend (both Neon and SVE) for FP16 vector
   operations - add, mul, sub, div, min, max, sqrt and fma.
   
   Testing:
   All JTREG tests - hotspot_all, jdk (tier 1-3) and langtools (tier 1)
   pass on aarch64 which also includes the JTREG test to test the FP16
   vector operations - test/hotspot/jtreg/compiler/vectorization/TestFloat16VectorOperations.java

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Changes: https://git.openjdk.org/jdk/pull/25096/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25096&range=03
  Stats: 1105 lines in 9 files changed: 426 ins; 0 del; 679 mod
  Patch: https://git.openjdk.org/jdk/pull/25096.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25096/head:pull/25096

PR: https://git.openjdk.org/jdk/pull/25096