[analyzer] Add modeling for unque_ptr::get()

Summary: Implemented  modeling for get() method in SmartPtrModeling

Reviewers: NoQ, Szelethus, vsavchenko, xazax.hun

Reviewed By: NoQ, xazax.hun

Subscribers: martong, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D86029