SI-1909 Move tests from pos to run

When we're in the neighbourhood of VerifyErrors, it's better to run
the code.

This change is leading up to a fix for SI-3832, which regressed
with fix for SI-1909.
SI-3832 Extract tracking of under-construction classes to a mixin

In order to reduce the noise in OuterPathTransformer.
SI-3832 Don't lift methods in aux constructor trailing stats as STATIC

SI-1909 modified LambdaLift to lift in auxiliary constructors methods as STATIC
so they could be called before the self-constructor was called.

That allowed for:

     class Foo (x: Int) {
       def this() = this( {
         def bar() = 5
         bar
       })
    }

However, if the method is in a statement that trails the self constructor call,
this is unnecessary and in fact incorrect as it robs the lifted method of `this`.

This commit uses the machinery established in SI-6666 to limit the STATIC-ness
of lifted methods to those used in arguments for self-constructor calls.
SI-1909 Predicate STATIC lifting on `isUnderConstruction` exclusively

The `isAuxillaryConstructor` check wasn't the right way to solve this,
as was seen by the regression it caused in SI-3832.