[vectorIntrinsics] RFR: 8261108: Add cast nodes from integer types to float types implementation for Arm SVE

[Wang Huang]

Add the backend codegen for nodes like castb2f / castb2d / casts2f / casts2d / casti2f / casti2d / castl2f / castl2d.

* add `sve_scvtf`  ( and `sve_ucvtf`) encoding
* add mock for these instructions
* add `VECTOR_CAST_I2F_EXTEND[N]` and `VECTOR_CAST_I2F`

Thank you for your review.

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Commit messages:
 - 8261108: Add cast nodes from integer types to float types implementation for Arm SVE

Changes: https://git.openjdk.java.net/panama-vector/pull/37/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=37&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261108
  Stats: 336 lines in 5 files changed: 274 ins; 0 del; 62 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/37.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/37/head:pull/37

PR: https://git.openjdk.java.net/panama-vector/pull/37