[data-flow] check for uninitialiazed values passed by pointer

[tonycoz]

Some APIs accept a pointer to an initialized object of some sort, check that such objects are initialized.

It might be possible do get clang-tidy to handle that itself by updating the declaration

[tonycoz]

sample clang static analyzer extension https://github.com/nsumner/clang-plugins-demo/blob/master/lib/streamchecker/SimpleStreamChecker.cpp