Check type for forward reference definition

The types of forward references are checked that they match with other
uses, but they do not check they match with the definition.

    func @forward_reference_type_check() -> (i8) {
      br ^bb2

    ^bb1:
      return %1 : i8

    ^bb2:
      %1 = "bar"() : () -> (f32)
      br ^bb1
    }

Would be parsed and the use site of '%1' would be silently changed to
'f32'.

This commit adds a test for this case, and a check during parsing for
the types to match.

Patch by Matthew Parkinson <mattpark@microsoft.com>

Closes D79317.