[foreign-abi] RFR: Turn on downcall intrinsics by default [v2]

[Jorn Vernee]

> Hi,
> 
> This PR turns on down call intrinsics by default.
> 
> Since the time they were turned off some fixes have been done in the area of GC handling of optimized native calls, and
> no further problems in that area have been found. What currently works is:
> 1. All TestDowncall and TestUpcall tests, where each function is invoked in a 20_000 iteration loop with -Xbatch,
> making sure these calls are intrinsified. 2. TestIntrinsics tests which intrinsifies calls the same way.
> 3. All jextract samples with intrinsics turned on, which from the logs also leads to calls being intrinsified,
> especially on large extraction runs like Windows.h.
> There is one more case that is known to be problematic: TestUpcallHighArity crashes/fails when the call is intrinsified
> (using same method as 1 and 2). This seems to be caused by a known problem with the handling on stack arguments for
> intrinsified calls. So, for now, intrinsification of calls that pass arguments on the stack will be turned off.  If
> there are other cases you would like to make sure work, please take the test for a spin.
> Thanks,
> Jorn

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev
excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since
the last revision:

 - Merge branch 'foreign-abi' into Default_Intrinsics
 - More stack tests
 - Enable intrinsics by default
 - Dissable intrinsics for stack arguments

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/354/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/354/files/e0486b10..8e6eb011

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=354&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=354&range=00-01

  Stats: 466 lines in 21 files changed: 223 ins; 85 del; 158 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/354.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/354/head:pull/354

PR: https://git.openjdk.java.net/panama-foreign/pull/354