Use expression mining independent of whether sygus stream is enabled (#8250)

Use expression mining independent of whether sygus stream is enabled (#8250)

Since it is possible to use SyGuS in incremental mode, e.g. for `get-abduct-next`, our expression mining, e.g. for filtering weak solutions, should apply independent of whether sygusStream is enabled.  This refactors the SyGuS solver so that we do so.