[clang][AST] RecursiveASTVisitor should visit owned TagDecl of friend type.

A FriendDecl node can have a friend record type that owns a RecordDecl
object. This object is different than the one got from TypeSourceInfo
object of the FriendDecl. When building a ParentMapContext this owned
tag decaration has to be encountered to have the parent set for it.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D131685