Properly name Nest structures with Nest_prefix (remove the typedefs that
don’t include this prefix).

Add C++ wrappers for some commonly used Nest types:
- NodeHandle
- NodeRange
- StringRef

Also adding unittests for these types

Also fix the operator<< location from Diagnostic.hpp; it need to be
outside of the Nest namespace, it order to be properly picked up.

All feather nodes are not fully contained in their corresponding classes

So far we mostly test expression

(also rename TypeBase into Type)