[Sema] Improve the error diagnostic for dot destructor calls on pointer objects

This commit improves the mismatched destructor type error by detecting when the
destructor call has used a '.' instead of a '->' on a pointer to the destructed
type. The diagnostic now suggests to use '->' instead of '.', and adds a fixit
where appropriate.

rdar://28766702

Differential Revision: https://reviews.llvm.org/D25817

llvm-svn: 292615