Fix typing of constants
This is an umbrella MR combining a few small changes:
- Fixes typing of constants.
If a typed
Constant
inside of an untypedConstantExpr
was encountered, the typification used to fail (see new test). - Strengthens
test_typify_integer_binops
now that arbitrary expressions can be deferred. - Increases the information content of two error messages.
- Fixes a typo.