c++: Don't suggest cdtor or conversion op identifiers in spelling hints [PR104806]

On the following testcase, we emit "did you mean '__dt '?" in the error
message.  "__dt " shows there because it is dtor_identifier, but we
shouldn't suggest those to the user, they are purely internal and can't
be really typed by the user because of the final space in it.

2022-03-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/104806
	* search.cc (lookup_field_fuzzy_info::fuzzy_lookup_field): Ignore
	identifiers with space at the end.

	* g++.dg/spellcheck-pr104806.C: New test.