[analyzer] Create generic SMT Sort Class

Summary:
New base class for all future SMT sorts.

The only change is that the class implements methods `isBooleanSort()`, `isBitvectorSort()` and `isFloatSort()` so it doesn't rely on `Z3`'s enum.

Reviewers: NoQ, george.karpenkov

Reviewed By: george.karpenkov

Subscribers: xazax.hun, szepet, a.sidorin

Differential Revision: https://reviews.llvm.org/D49550

llvm-svn: 337916