[multi-modules] Copy KDoc from base symbols into inherited symbols

[martinbonnin]

There's a nice feature that when a symbol doesn't define its KDoc, the one from the overriden/subclassed symbol is used instead.

This works well when everything is in the same module:

interface Greeter {
  /**
   * Says hello 👋
   *
   * @return a string that says hello
   */
  fun hello(): String
}

class EnglishGreeter: Greeter {
  override fun hello(): String {
    return "Hello \uD83D\uDC4B"
  }
}

Now when crossing the module boundary, this doesn't work anymore:

class FrenchGreeter : Greeter {
    override fun hello(): String {
        return "Bonjour"
    }
}

Reproducer available here.

This is probably related to #1960 but since this one is about inheriting KDoc specifically, I thought I would open a new one in case someone else bumps into this.

[whyoleg]

Hey!
This is a known issue:

• for KDoc defined in another module of multi-module project: Use sources of dependent submodules instead of their artifacts #3249
• for KDoc defined in external dependencies: Provide a way to supply source files of external dependencies for inheriting documentation #463

There is possible workaround (or at least an idea for it) in a comment here: #463 (comment)