[analyzer] Moved code from SMTConstraintManager to SMTSolver

Summary:
This is the second part of D49668, and moves all the code that's not specific to a ConstraintManager to SMTSolver.

No functional change intended.

Reviewers: NoQ, george.karpenkov

Reviewed By: george.karpenkov

Subscribers: xazax.hun, szepet, a.sidorin

Differential Revision: https://reviews.llvm.org/D49767

llvm-svn: 337921