Use actual scalar type instead of metadata scalar type for generated C# properties

[amwebb]

The C# metadata code generator should create properties for metadata fields that use C# scalar types instead of metadata scalar types.

For example, the title field of document should have a property:

public string Title
{
get { return title; }
set {title = value; }
}

instead, it currently generates the following:

public MetadataString Title { ... }