[Analyzer] Support note tags for smart ptr checker

Summary:
Added support for note tags for null smart_ptr reporting

Reviewers: NoQ, Szelethus, vsavchenko, xazax.hun

Reviewed By: NoQ, vsavchenko, xazax.hun

Subscribers: martong, cfe-commits
Tags: #clang

Differential Revision: https://reviews.llvm.org/D84600