[vectorIntrinsics] RFR: 8263644: Add Extract float nodes implementation for Arm SVE [v2]

[Xiaohong Gong]

On Mon, 22 Mar 2021 07:08:11 GMT, Wang Huang <whuang at openjdk.org> wrote:

>> We implement ExtractD & ExtractF Node for Arm SVE backend.
>> * overload encoding functions `sve_lasta` & `sve_lastb`
>> * for future JDK-8263424, we eliminate vector length judgements and use  `rscratch1`
>
> Wang Huang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   refact some codes

Marked as reviewed by xgong (no project role).

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PR: https://git.openjdk.java.net/panama-vector/pull/51