Fix GC holes in array marshallers in the field scenario (dotnet/coreclr#27562)

Fix GC holes in array marshallers in the field scenario (dotnet/coreclr#27562)

* Correctly protect references to objects in manually-managed code called by IL marshalers in the field scenarios. Use RuntimeHelpers.GetRawData to simplify layout class marshalling.

* Add additional protects for SAFEARRAY marshalling when used in the field scenario.

* Remove dead code.

* Fix possible GC hole from order of argument evaluation.

* Don't clean up fields on a managed object when there's no managed object.

Commit migrated from https://github.com/dotnet/coreclr/commit/e658b97990f77dca2dba446386e9d8d4d71556e1