[analyzer][UninitializedObjectChecker] Pointer/reference objects are...

[analyzer][UninitializedObjectChecker] Pointer/reference objects are dereferenced according to dynamic type

This patch fixed an issue where the dynamic type of pointer/reference
object was known by the analyzer, but wasn't obtained in the checker,
which resulted in false negatives. This should also increase reliability
of the checker, as derefencing is always done now according to the
dynamic type (even if that happens to be the same as the static type).

Special thanks to Artem Degrachev for setting me on the right track.

Differential Revision: https://reviews.llvm.org/D49199

llvm-svn: 339240