Perform theory widening eagerly (#4044)

Perform theory widening eagerly (#4044)

Fixes #3971 and fixes #3991. In incremental mode, the logic can change from one
(check-sat) call to another. In the reported issue, we start with QF_NIA
but then switch to QF_UFNIA because there is a div term (which has a UF in
its expanded form). Dealing with this issue is challenging in general. As a
result, we have decided not to allow theory widening in
Theory::expandDefinitions() anymore but instead to do it eagerly in
SmtEngine::setDefaults().