C++ interface: print protected constructors before public ones
C++ interface: print protected constructors before public ones

This matches the order of the constructor declarations
in plain_cpp_generator::print_class, making it easier
to extract out a shared print_public_methods in the next commit.

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl