[foreign-memaccess+abi] RFR: 8301262: Simplify the CaptureCallState support

[Jorn Vernee]

Simplify capture call state support based on Maurizio's suggestion.

We currently compute a layout to write the captured state into based on the values that the user wants to capture. However, we could simplify the API by using the same layout every time, that can hold every value that someone might want to capture. This is only 12 bytes, so the memory usage is not a big deal. The important part is to not read every thread local value every time, which works just as it does today.

The second issue in today's implementation, is that it is still possible to create a capture state linker option that captures `GetLastError` on Linux. But, this doesn't make any sense. In the new implementation the GetLastError and WSAGetLastError options are only available on Windows.

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Commit messages:
 - doc tweaks
 - fix linux
 - Simplify captureCallState API

Changes: https://git.openjdk.org/panama-foreign/pull/778/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=778&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301262
  Stats: 177 lines in 9 files changed: 80 ins; 73 del; 24 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/778.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/778/head:pull/778

PR: https://git.openjdk.org/panama-foreign/pull/778