feat(library/elaborator): add special treatment for constraints of the form ?m[inst:i v] << t, where t is a proposition

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/parser): display failed state in noninteractive mode, stop processing tactic commands when a Lean command is found

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>