[Clang][Sema] Fix bug where operator-> typo corrects in the current instantiation (#91972)

#90152 introduced a bug that occurs when typo-correction attempts to fix a reference to a
non-existent member of the current instantiation (even though
`operator->` may return a different type than the object type). This
patch fixes it by simply considering the object expression to be of type
`ASTContext::DependentTy` when the arrow operator is used with a
dependent non-pointer non-function operand (after any implicit
conversions).