Renames Type to OpType in VisualShaderNodeMultiplyAdd

[Chaosus]

To prevent possible conflicts with C# and other languages.

[Chaosus]

However, there are some other classes with "get_type" :

I tested it with C# and notice that object.GetType is just getting replaced by the custom GetType with no conflicts (but this prevents usage of common GetType). I'm not sure whether this change is really needed, or it's needed for all of these classes too, cc @neikeq

[neikeq]

I'm not against this rename, but IMO we should make the C# bindings generator detect the name and change it to GetType_ or something else.

[aaronfranke]

@Chaosus Please see #36382 for renaming other instances of type and get_type and more.

[akien-mga]

Thanks!