godot: Using most System.IO file classes will crash on iOS devices (not in the simulator)

Godot version: 3.2.2 Mono w/ Mono 6.10 stable

OS/device including version: Build w/ OSX Catalina, tested on various iPhones w/ iOS 13

Issue description: App will crash when using most of the System.IO classes, such as File or FileStream. This only happens on real devices. The simulator works fine.

The crash occurs any time the framework needs to call the native Stat method to check if a file exists (and most of the File classes do this on creation to know whether to overwrite, append, or throw depending on modes passed).

SystemNative_Stat2
  at Interop+Sys.Stat (System.ReadOnlySpan`1[T] path, Interop+Sys+FileStatus& output)
  at System.IO.FileSystem.FileExists (System.ReadOnlySpan`1[T] fullPath, System.Int32 fileType, Interop+ErrorInfo& errorInfo)
  at System.IO.FileSystem.DirectoryExists (System.ReadOnlySpan`1[T] fullPath, Interop+ErrorInfo& errorInfo)
  at System.IO.FileSystem.DirectoryExists (System.ReadOnlySpan`1[T] fullPath)
  at System.IO.Directory.Exists (System.String path)
  at System.IO.FileStream..ctor (System.String path, System.IO.FileMode)

As with #40633, I am unsure whether this is a problem with the way Godot is using Mono, a symptom of AoT (required for iOS), or a problem with the Mono implementation on iOS. I am starting to think it’s related and that’s its a linking or packaging problem for native methods on iOS.

It’s not clear to me which versions of libmono get packed if your local Mono install doesn’t match the pre-compiled export template (in my case 6.10 vs 6.8). I also tried this matching my local Mono version to the template. The issue still occurred.

Steps to reproduce:

1. Open a file in OpenCreate modes (other modes should also trigger this). e.g. new FileStream(Path.Combine(".test"), FileMode.OpenOrCreate);

Minimal reproduction project: Test-MonoFileIOS.zip