Use symbol manager for printing responses get-model (#5516)

Use symbol manager for printing responses get-model (#5516)

This makes symbol manager be in charge of determining which sorts and terms to print in response to get-model. This eliminates the need for the parser to call ExprManager::mkVar (and similar methods) with custom flags.

This requires significant simplifications to the printers for models, where instead of a NodeCommand, we take a Sort or Term to print in the model.

This is one of the last remaining steps for migrating the parser to the new API.

The next step will be to remove a lot of the internal infrastructure for managing expression names, commands to print in models, node commands, node listeners, etc.