When extracting members, get them from single file only

When extracting members, get them from single file only

The previous commit fixed the situation when e.g. anon_struct_0 was in the
current file by checking the current file first.

In the case the struct type definition isn't found in the current file,
at the moment we get all members from all anon_struct_0 which can be a
really long list. This list isn't very helpful to users because all the
members from all the structs are mixed. Moreover, not all possible members
are in the list because there are e.g. just members from anon_struct_0 but
not from anon_struct_1 etc. which from the point of view of this function
is a different type.

Instead, restrict the returned members to just a single file (anonymous
structs have unique name per file so it means there will be just one
from the file). Of course the picked file can be wrong and the returned
members might be from a different struct the user wanted but at least
the list will make more sense to users.