Add support for emitting finally regions in ILEmitter (dotnet/coreclr#27109)

Add support for emitting finally regions in ILEmitter (dotnet/coreclr#27109)

This will be needed to properly do cleanups in marshalling stubs.

The usage goes like (I couldn't come up with anything better):

```
var b = codeStream.BeginTry();
//...
codeStream.EndTry(b);
codeStream.BeginHandler(b);
// ...
codeStream.EndHandler(b);

emit.NewFinallyRegion(b);
```

Commit migrated from https://github.com/dotnet/coreclr/commit/a7ffbba5a2843e7da03fdffe40ac85b9adfe126e