Fix closed delegate deserialization to account for extension methods (dotnet/coreclr...

Fix closed delegate deserialization to account for extension methods (dotnet/coreclr#10901)

Functional fix for dotnet/coreclr#9597:
- The code was incorrectly assuming that the serialized target type info refers to the target object's type; it actually refers to the method's reflected type, which may not be the same type when it's an extension method

Commit migrated from https://github.com/dotnet/coreclr/commit/45d0444a05f0bbceb2f259ce483c080f0991be1b