[vectorIntrinsics] RFR: 8261108: Add cast nodes from integer types to float types implementation for Arm SVE [v2]

[Wang Huang]

On Sat, 20 Feb 2021 02:06:37 GMT, Ningsheng Jian <njian at openjdk.org> wrote:

>> `T_dst` and `T_src` will be changed after  `encode_cvtf_T`, so they cannot move there.
>
> I think it's fine to assign the values at the beginning. And maybe you can add more test cases to check different combinations.

I have added some comments here to explain codes here.

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