[vectorIntrinsics] RFR: 8267224: Vector API SVE codegen cleanups

[Ningsheng Jian]

Some code cleanups for SVE: 

- Revert sve_dup assembler changes, as well as similar changes to sve_cpy assembler. See [1].
- Refactor fcvt/fcvtzs/scvtf assembler code.
- Add more assembler tests to make sure the coverage for newly added assembler routines.
- Fix gather/scatter addressing issue.
- Some code style cleanups.
- Merge some matching patterns.

[1] https://github.com/openjdk/jdk/pull/1307

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Commit messages:
 - 8267224: Vector API SVE codegen cleanups

Changes: https://git.openjdk.java.net/panama-vector/pull/82/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=82&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267224
  Stats: 633 lines in 8 files changed: 77 ins; 207 del; 349 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/82.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/82/head:pull/82

PR: https://git.openjdk.java.net/panama-vector/pull/82