[analyzer] MoveChecker: Add checks for dereferencing a smart pointer after move.

Calling operator*() or operator->() on a null STL smart pointer is
undefined behavior.

Smart pointers are specified to become null after being moved from.
So we can't warn on arbitrary method calls, but these two operators
definitely make no sense.

The new bug is fatal because it's an immediate UB,
unlike other use-after-move bugs.

The work on a more generic null smart pointer dereference checker
is still pending.

Differential Revision: https://reviews.llvm.org/D55388

llvm-svn: 349226