chore(tactic/interactive): propagate tags in `substs` (#6638)
Before this change, the `case left` tactic here did not work:
```lean
example {α : Type*} (a b c : α) (h : a = b) : (a = b ∨ a = c) ∧ true :=
begin
with_cases {apply and.intro},
substs' h,
case left : { exact or.inl rfl },
case right : { trivial }
end
```
