[foreign-memaccess+abi] RFR: 8275647: Enable multi-register return values for optimized upcall stubs

[Jorn Vernee]

Hi,

After we've added multi-register return support to native invokers, this patch does the same for optimized upcall stubs. The strategy is very similar: the caller (in this case the upcall stub) allocates a return buffer in which the return values are stored, and then after the upcall shuffles the return values from the buffer into the right registers.

This patch also removes the buffered invocation strategy for upcalls, and all related code, such as BufferLayout.

~Note, in it's current state this patch will disable regress AArch64 since optimized upcalls are not implemented there yet. i.e. this PR is blocked by: https://bugs.openjdk.java.net/browse/JDK-8275646~

Jorn

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Commit messages:
 - fix receiver name
 - - AArch64 first impl
 - Cast to OptimizedEntryBlob after null check
 - Rename 'imr' + RB fixes
 - Remove some left-over buffered invocation code.
 - Clean up free upcall stubs
 - Remove the buffered invocation strategy
 - Implement upcall IMR specialization
 - Implement multi-register returns for upcalls (on x86_64) - interpreted only

Changes: https://git.openjdk.java.net/panama-foreign/pull/608/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=608&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275647
  Stats: 1167 lines in 32 files changed: 268 ins; 808 del; 91 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/608.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/608/head:pull/608

PR: https://git.openjdk.java.net/panama-foreign/pull/608