[foreign-memaccess+abi] RFR: 8275644: Replace VMReg in shuffling code with something more fine grained. [v4]

[Jorn Vernee]

> This patch replaces `VMReg` with a new `VMStorage` class in the C++ code, which can be used to represent stack arguments of different sizes, as well as allowing finer grained stack addressing.
> 
> The old masm code that used `VMReg` for moving values is also replaced with new code that uses `VMStorage`. And `VMReg` is changed to `VMStorage` everywhere.
> 
> The `vmstorageBase` class was added in C++ to mirror the `jdk.internal.foreign.VMStorage`. That class now also has an additional field to encode the size of a stack argument, or a register mask, which can also be used to encode the size of a register argument. This also leads to some stubs needing to be updated on unsupported platforms.
> 
> Lastly, instead of encoding stack indexes as 64-bit slots as we did before, they are now encoded as byte offsets, which allows finer grained stack addressing. (this leads to a bunch of values being multiplied by 8 in the Java code as well).
> 
> ---
> 
> This change is needed to address https://bugs.openjdk.org/browse/JDK-8275584 as well as adding support for `long double` as well as more exotic ABIs that take arguments as vectors.

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 22 commits:

 - Merge branch 'foreign-memaccess+abi' into VMStorage2
 - remove spurious include
 - rename index -> indexOrOffset
 - revert spurious merge change
 - Fix stack arg allocation
 - Relax stack storage checking
 - Polish
 - Uncouple VMStorage from current Architecture
 - Merge branch 'VMStorage2' of https://github.com/JornVernee/panama-foreign into VMStorage2
 - Stubs2
 - ... and 12 more: https://git.openjdk.org/panama-foreign/compare/60e656e0...9cdabd8a

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Changes: https://git.openjdk.org/panama-foreign/pull/699/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=699&range=03
  Stats: 1420 lines in 46 files changed: 799 ins; 130 del; 491 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/699.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/699/head:pull/699

PR: https://git.openjdk.org/panama-foreign/pull/699