fix code generation when dereferencing pointers (ref_to) to arrays (ref_to_array^[5])

Fix bug: set the scope annotation in deref_operators used inside structs

Editing of error message to make it more clear.

Filling of symbol->scope annotation moved from narrow to fill_candidate_datatypes_c (became possible because narrowing of struct, array and symbolic variables is now done directly in fill_candidate_datatypes_c)

fill_candidate_datatypes_c now uses search_varinstance_decl_c instead of search_varfb_instance_type_c (moving towards deprecation of search_varfb_instance_type_c)

Do the full fill_candidate/narrow_datatype algorithm for all fields of a structured variable in the fill_candidate_datatypes_c
Allows us to remove temporary code from the search_varfb_decl_c

Fix bug with multple dereferencing (bool_var := bool_ptr_ptr^^;)

Fix bug: Add support for de-referencing pointers to struct (struct_ptr^.elem1) when used inside FB.
Note that multiple de-referencing of structs (struct_ptr_ptr^^.elem) is not supported inside FB code (this would need BIG changes to the compiler!)

Fix bug: add support for dereferencing of REF_TO to REF_TO xxx (e.g.: bool_var := ref_to_ref_to_bool^^;)

Turn support of derefencing operator '^' an option (default is not supported).