[foreign-jextract] RFR: 8248415: Create VarHandles for pointer fields through the MemoryHandles API [v2]

[Filip Krakowski]

> This PR creates an adapted
> [`VarHandle`](https://github.com/openjdk/panama-foreign/blob/foreign-jextract/src/java.base/share/classes/java/lang/invoke/VarHandle.java)
> usable with
> [`MemoryAddress`](https://github.com/openjdk/panama-foreign/blob/foreign-jextract/src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/MemoryAddress.java)
> carriers for pointer fields. It uses
> [`MemoryHandles#asAddressVarHandle`](https://github.com/openjdk/panama-foreign/blob/foreign-jextract/src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/MemoryHandles.java#L334-L350)
> and a previously created `long` VarHandle to do so.

Filip Krakowski has updated the pull request incrementally with one additional commit since the last revision:

  Fix some carrier entries within carrier map

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/216/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/216/files/3596f8da..20c33711

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/216/webrev.01
 - incr: https://webrevs.openjdk.java.net/panama-foreign/216/webrev.00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/216.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/216/head:pull/216

PR: https://git.openjdk.java.net/panama-foreign/pull/216