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

[Wang Huang]

> 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

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Changes:
  - all: https://git.openjdk.java.net/panama-vector/pull/51/files
  - new: https://git.openjdk.java.net/panama-vector/pull/51/files/8b70753a..630a2675

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=51&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=51&range=00-01

  Stats: 10 lines in 2 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/51.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/51/head:pull/51

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