[analyzer][UninitializedObjectChecker] PR41741: Regard all scalar types as primitive.

https://bugs.llvm.org/show_bug.cgi?id=41741

Pretty much the same as D61246 and D61106, this time for __complex__ types. Upon
further investigation, I realized that we should regard all types
Type::isScalarType returns true for as primitive, so I merged 
isMemberPointerType(), isBlockPointerType() and isAnyComplexType()` into that
instead.

I also stumbled across yet another bug,
https://bugs.llvm.org/show_bug.cgi?id=41753, but it seems to be unrelated to
this checker.

Differential Revision: https://reviews.llvm.org/D61569

llvm-svn: 359998