RFR: 8287289: Gather/Scatter with Index Vector [v2]

[Quan Anh Mai]

> Hi,
> 
> This patch implements gather/scatter operations using an index vector in the form of an `IntVector` or a `LongVector` on arrays and memory segments. According to the rationales in the [original PR](https://github.com/openjdk/panama-vector/pull/201), gathering/scattering using a vector is more flexible and can be used to implement the original interface of using an index array easily. Furthermore, 64-bit indexing is necessary for operating on `MemorySegment`s, which can span a larger-than-4GiB space.
> 
> Please take a look and leave reviews.
> Thanks a lot.

Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:

  check index vector

-------------

Changes:
  - all: https://git.openjdk.org/panama-vector/pull/213/files
  - new: https://git.openjdk.org/panama-vector/pull/213/files/7c1a8889..e5497060

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-vector&pr=213&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-vector&pr=213&range=00-01

  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/panama-vector/pull/213.diff
  Fetch: git fetch https://git.openjdk.org/panama-vector.git pull/213/head:pull/213

PR: https://git.openjdk.org/panama-vector/pull/213