Revert "Reland "[vm/ffi] Disallow `Pointer`s and structs in finalizers and expandos""

This reverts commit 3f0ad61daaac68e591bf01d0a3096926c30c1d42.

Reason for revert: Conflicts with https://dart-review.googlesource.com/c/sdk/+/194765

Original change's description:
> Reland "[vm/ffi] Disallow `Pointer`s and structs in finalizers and expandos"
>
> `Dart_NewWeakPersistentHandle` and `Dart_NewFinalizableHandle` in
> `dart_api.h` do no longer accept `Pointer`s and subtypes of `Struct`s
> as values passed in to the `object` parameter.
>
> Expandos no longer accept `Pointer`s and subtypes of `Struct`s
> as values passed in to the `object` parameter.
>
> Cleans up unused object_store->ffi_struct_class.
>
> Closes: https://github.com/dart-lang/sdk/issues/45071
> Breaking change: https://github.com/dart-lang/sdk/issues/45072
>
> TEST=vm/cc/DartAPI_FinalizableHandleErrors
> TEST=vm/cc/DartAPI_WeakPersistentHandleErrors
> TEST=tests/ffi(_2)/expando_test.dart
>
> Change-Id: I9af6d0173db60614091068c218391f73756c135f
> Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/195061
> Reviewed-by: Martin Kustermann <kustermann@google.com>
> Commit-Queue: Daco Harkes <dacoharkes@google.com>

TBR=kustermann@google.com,dacoharkes@google.com

Change-Id: I90064b6b73155a43f37388f987c6b29f72ce9770
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/195076
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>