Separators of operations are parsed inconsistently

The following program using a space to separate two operations (both in their definition and implementation) is currently syntactically valid:
```scala
interface Foo { def foo(): Int def bar(): Int }
def main() =
try { do foo() + do bar() }
with Foo { def foo() = resume(42) def bar() = resume(100) }
```

Proof

Inserting semicolons in order to separate the two operations is **not** allowed: neither in their definition, nor in their implementation.

---

In contrast, if you write:
```scala
type Quux { Bar() Baz() }
```
then you actually **must** insert a semicolon or a newline to get a successful parse.