fix(library/unifier): bug introduced today in consume_tc_cnstrs

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard): add or_inl and or_inr as short-hands for the commonly used 'or_intro_left _' and 'or_intro_right _'

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