[hot_reload] Fix unresolved token when new nested structs are used

[lambdageek]

When a hot reload delta contains a new nested struct that is used as a field in a newly-added class, the metadata delta adds the field of the enclosing class before it adds the fields of the nested struct. As a result, resolving the token of the field of the enclosing struct too early will make the runtime think that the nested struct has 0 fields and subsequent field lookups will fail.

Example:

Original Code:

public class C {
  public void ExistingMethod() { }

Delta code:

public class C {
  public void ExistingMethod() {
    new AddedClass();
  }
}

public class AddedClass {
  public NestedStruct Field1;
  public AddedClass() {
    Field1 = new NestedStruct { D = 1.0 };
  }
  public struct NestedStruct {
    public double D;
  }
}

Expected result:
Applying the hot reload delta succeeds

Actual result:

System.BadImageFormatException: Could not resolve field token 0x04000014

[lambdageek]

I'd like to backport this to .NET 7

[lambdageek]

/backport to release/7.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3184163210

[lambdageek]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[lambdageek]

Wasm debugger failure is #64188