`posTwice` `testNonCyclic` fails if `dotc.CompilationUnit` does not import `Types.Type`

[nicolasstucki]

If we remove the unused import import dotty.tools.dotc.core.Types.Type in dotty.tools.dotc.CompilationUnit the testNonCyclic fails in posTwice.

-- [E006] Unbound Identifier Error: ../compiler/src/dotty/tools/dotc/ast/Trees.scala:817:42 
817 |  abstract class Instance[T >: Untyped <: Type] extends DotClass { inst =>
    |                                          ^^^^
    |                                          not found: type Type

Note that the error manifests itself in another class.

[nicolasstucki]

#3778 showed that this issue is not completely fixed. Now testNonCyclic passes but testIssue34 fails (http://dotty-ci.epfl.ch/lampepfl/dotty/2372/4).

[nicolasstucki]

To consider this issue as fixed we should include 354e2eb.