RFR: 8356869: RISC-V: Improve tail handling of array fill stub

[Anjian-Wen]

The tail handling after bulk copy in array fill stub may trigger misaligned memory accesses.
The address is 8-byte aligned after bulk copy and the tail handling copies BYTE, SHORT, and
INT granules in order. This could trigger misaligned accesses. We should copy the remainings
in this order: INT, SHORT, and BYTE to avoid such an issue.

JMH data on P550 SBC for reference (@Param("15") private int size):

Before:
Benchmark                 (size)  Mode  Cnt    Score   Error  Units
ArrayFill.fillByteArray       15  avgt   12  961.604 ± 1.497  ns/op
ArrayFill.fillIntArray        15  avgt   12   29.355 ± 0.024  ns/op
ArrayFill.fillShortArray      15  avgt   12  569.499 ± 0.662  ns/op
ArrayFill.zeroByteArray       15  avgt   12  957.080 ± 5.358  ns/op
ArrayFill.zeroIntArray        15  avgt   12   29.344 ± 0.006  ns/op
ArrayFill.zeroShortArray      15  avgt   12  569.730 ± 0.441  ns/op

After:
Benchmark                 (size)  Mode  Cnt   Score   Error  Units
ArrayFill.fillByteArray       15  avgt   12  32.206 ± 0.005  ns/op
ArrayFill.fillIntArray        15  avgt   12  29.347 ± 0.007  ns/op
ArrayFill.fillShortArray      15  avgt   12  31.732 ± 0.451  ns/op
ArrayFill.zeroByteArray       15  avgt   12  32.208 ± 0.007  ns/op
ArrayFill.zeroIntArray        15  avgt   12  29.346 ± 0.007  ns/op
ArrayFill.zeroShortArray      15  avgt   12  31.492 ± 0.006  ns/op

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Commit messages:
 - RISCV: fix alignment of generate_fill after fill_word

Changes: https://git.openjdk.org/jdk/pull/25210/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25210&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356869
  Stats: 19 lines in 1 file changed: 5 ins; 5 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/25210.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25210/head:pull/25210

PR: https://git.openjdk.org/jdk/pull/25210