fix(kernel/converter): missing constraints

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/unifier): process_flex_rigid method before adding yet another case split

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/error_handling): add flycheck_scope helper class

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