Detect when resolve needs ModuleRef when likely cyclic references

[myyk]

This completes #3715 with all the cycle cases I could think of.

It also touches resolveDirectChildren where I made some changes that I would help with readability. I thought I was going to need to build on those but didn't. These can be reverted if it's unwanted.

[myyk]

I added some cycle detection for the direct dependencies but I'm stuck on cases when it's foo.__.bar-shaped where foo or bar can be anything, even _.

You can run the tests with ./mill main.resolve.test:

[960-2] ----------------------------------- Failures -----------------------------------
[960-2] X mill.resolve.ResolveTests.nested.wildcard3 3ms 
[960-2]   utest.AssertionError: resolvedTasks.map(_.map(_.toString).toSet[String]) ==
[960-2]   resolvedTasks: Either[String,List[mill.define.NamedTask[Any]]] = Left(Cyclic module reference detected: [class mill.util.TestGraphs$nestedModule$classInstance$], it's required to wrap it in ModuleRef.
[960-2]   Cyclic module reference detected: [class mill.util.TestGraphs$nestedModule$nested$], it's required to wrap it in ModuleRef.)
[960-2]   expected: scala.util.Either[String,scala.collection.immutable.Set[mill.define.NamedTask[Any]]] = Right(Set(classInstance.single, nested.single))
[960-2]     utest.asserts.Asserts$.assertImpl(Asserts.scala:30)
[960-2]     mill.resolve.ResolveTests$Checker.checkSeq(ResolveTests.scala:25)
[960-2]     mill.resolve.ResolveTests$Checker.apply(ResolveTests.scala:15)
[960-2]     mill.resolve.ResolveTests$.$anonfun$tests$66(ResolveTests.scala:230)
[960-2] X mill.resolve.ResolveTests.cross.double.wildcard.labelNeg4 3ms 
[960-2]   utest.AssertionError: resolvedTasks.map(_.map(_.toString).toSet[String]) ==
[960-2]   resolvedTasks: Either[String,List[mill.define.NamedTask[Any]]] = Left(Cyclic module reference detected: [class mill.util.TestGraphs$doubleCross$cross$], it's required to wrap it in ModuleRef.)
[960-2]   expected: scala.util.Either[String,scala.collection.immutable.Set[mill.define.NamedTask[Any]]] = Left(Cannot resolve cross.__.doesntExist. Try `mill resolve cross._` to see what's available.)
[960-2]     utest.asserts.Asserts$.assertImpl(Asserts.scala:30)
[960-2]     mill.resolve.ResolveTests$Checker.checkSeq(ResolveTests.scala:25)
[960-2]     mill.resolve.ResolveTests$Checker.apply(ResolveTests.scala:15)
[960-2]     mill.resolve.ResolveTests$.$anonfun$tests$113(ResolveTests.scala:365)
[960-2] Tests: 161, Passed: 159, Failed: 2

It's showing these 2 false positives because those are not cycles. These are the only noncyclic foo.__.bar test cases in there and I think that's the commonality.

[myyk]

The cleanup looks good to me

[lihaoyi]

Thanks @myyk! I'll close out the bounty over whatsapp