millModuleDirectChildren is not respected when resolving

[lolgab]

Given this build:

import mill._
object mod extends Module {
  override lazy val millModuleDirectChildren = Seq.empty[Module]
  object bar extends Module
  object foo extends Module
}

mill resolve mod._

returns mod.bar and mod.foo in 0.11.0-M11 while doesn't return anything in 0.10.12

[lefou]

The following PRs might contain that change:

• More refactoring for Resolve logic #2511
• Make mill.define.Module a trait to allow abstract/virtual module lazy vals to be traits rather than classes #2536
• Clean up Resolve.scala and related code to improve rigor and error reporting #2453

[lihaoyi]

The new resolver aims to avoid instantiating things as far as possible, so it doesn't even look at millModuleDirectChildren and just uses the java.lang.Class for resolution.

We can make this work again by introducing a marker trait, perhaps DynamicChildren, to indicate to Mill that we should actually instantiate the module and look at its children. This would be similar to what we do for Cross modules

[lolgab]

What I really need is a def enabled: Boolean = true in Module so users and plugins can dynamically disable modules based on conditions. Redefining millModuleDirectChildren was what was possible in Mill 0.10.