[vectorIntrinsics] RFR: 8262492: Add cast nodes between float types implementation for Arm SVE

[Wang Huang]

Add cast nodes like castf2d castd2f

* add `sve_fcvt`
* reuse macro `VECTOR_CAST_I2F_NARROW1` `VECTOR_CAST_I2F_EXTEND1` (Should we change the macro names?)

other issues :
* precision loss

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Commit messages:
 - 8262492: Add cast nodes between float types implementation for Arm SVE

Changes: https://git.openjdk.java.net/panama-vector/pull/41/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=41&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262492
  Stats: 151 lines in 5 files changed: 84 ins; 4 del; 63 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/41.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/41/head:pull/41

PR: https://git.openjdk.java.net/panama-vector/pull/41