[foreign-memaccess] RFR: 8252504: Add a method to MemoryLayout which returns a offset-computing method handle [v2]

[Jorn Vernee]

> This PR adds two new methods: `bitOffsetHandle` and `byteOffsetHandle` to `MemoryLayout`, that can be used to create method handles that can compute the effective offset of a layout element given a set of additional `long` indexes.
> 
> I also cleaned up a leftover in the javadoc of bitOffset and byteOffset where an API note was stating that `sequenceElement()` layout path elements would be interpreted as `sequenceElement(0)`, but they were actually being rejected outright (as they should).
> 
> I also added some tests to cover the corner case where an UnsupportedOperationException was being thrown. (some of the churn in the tests is from introducing static imports. I hope it's not too noisy).

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:

 - Merge branch 'foreign-memaccess' into OffsetHandle
 - Touch up javadoc v1
 - Simplify impl to use strides array
 - Add test with multiple indexes
 - Add positive byteOffsetHandle test, and test that tests a bit offset that is not a multiple of 8
 - Polish impl
 - Remove unused imports
 - Added more tests, touched up javadoc
 - WIP - javadoc
 - WIP

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Changes: https://git.openjdk.java.net/panama-foreign/pull/396/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=396&range=01
  Stats: 315 lines in 4 files changed: 256 ins; 7 del; 52 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/396.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/396/head:pull/396

PR: https://git.openjdk.java.net/panama-foreign/pull/396