refactor(kernel/expr): value deserializer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(kernel/builtin): move builtin declarations to basic

There is a lot to be done. We should do the same for Nat, Int and Real.
We also should cleanup the file builtin.cpp and builtin.h.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(kernel/builtin): move builtin declarations to basic