[clang] Add test for CWG405

P1787: //CWG405 is resolved by stating that argument-dependent lookup (sometimes) occurs after an ordinary unqualified lookup (making statements like “finding a variable prevents argument-dependent lookup” formally correct).//
Wording: see changes to [basic.lookup.argdep] p1 and p3

This issue seems a duplicate of CWG218, even though it is not officially recognized. A part of a test for CWG218 is reused here, adding cross-references.

Reviewed By: #clang-language-wg, aaron.ballman

Differential Revision: https://reviews.llvm.org/D139095