[jdk22u] RFR: 8318158: RISC-V: implement roundD/roundF intrinsics [v2]

[Olga Mikhaltsova]

> I would like to backport [JDK-8318158](https://bugs.openjdk.org/browse/JDK-8318158) to jdk22u in order to optimize performance in double/float rounding operations by means of intrinsics.
> The patch applied cleanly.
> Tested: no regression in tier1 tests.
> 
> The benchmark shows the following performance improvement on the T-Head RVB-ICE board:
> **Before**
> 
> Benchmark                              (TESTSIZE)   Mode  Cnt    Score   Error   Units
> FpRoundingBenchmark.test_round_double        2048  thrpt   15   59.722  0.259  ops/ms
> FpRoundingBenchmark.test_round_float         2048  thrpt   15   49.729  0.127  ops/ms
> 
> **After**
> 
> Benchmark                              (TESTSIZE)   Mode  Cnt    Score   Error   Units
> FpRoundingBenchmark.test_round_double        2048  thrpt   15  118.496  0.277  ops/ms
> FpRoundingBenchmark.test_round_float         2048  thrpt   15  121.008  0.488  ops/ms

Olga Mikhaltsova has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into backport-omikhaltsova-19147f32
 - Backport 19147f326c6b0e78fe72f9a7e7100047f16a0921

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

Changes:
  - all: https://git.openjdk.org/jdk22u/pull/21/files
  - new: https://git.openjdk.org/jdk22u/pull/21/files/aa33e2a5..1e021623

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk22u&pr=21&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk22u&pr=21&range=00-01

  Stats: 6 lines in 2 files changed: 5 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk22u/pull/21.diff
  Fetch: git fetch https://git.openjdk.org/jdk22u.git pull/21/head:pull/21

PR: https://git.openjdk.org/jdk22u/pull/21