[analyzer] PR41269: Add a bit of C++ smart pointer modeling.

[analyzer] PR41269: Add a bit of C++ smart pointer modeling.

Implement cplusplus.SmartPtrModeling, a new checker that doesn't
emit any warnings but models methods of smart pointers more precisely.

For now the only thing it does is make `(bool) P` return false when `P`
is a freshly moved pointer. This addresses a false positive in the
use-after-move-checker.

Differential Revision: https://reviews.llvm.org/D60796

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@358944 91177308-0d34-0410-b5e6-96231b3b80d8