[jdk19u] RFR: 8293100: RISC-V: Need to save and restore callee-saved FloatRegisters in StubGenerator::generate_call_stub

[Vladimir Kempik]

Please review this backport to jdk19u.
This fixes critical error in call_stub in risc-v
APplies almost clean. Slightly different class names in surrounding code ( in vmreg_riscv.cpp ) prevents it being clean.

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Commit messages:
 - 8293100: RISC-V: Need to save and restore callee-saved FloatRegisters in StubGenerator::generate_call_stub

Changes: https://git.openjdk.org/jdk19u/pull/19/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19u&pr=19&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293100
  Stats: 81 lines in 4 files changed: 64 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk19u/pull/19.diff
  Fetch: git fetch https://git.openjdk.org/jdk19u pull/19/head:pull/19

PR: https://git.openjdk.org/jdk19u/pull/19