Investigate supporting implicit GraphExtension factory functions

[ZacSweers]

Description

Originally mentioned in #1872, it turns out dagger allows declaring a subcomponent accessor function with parameters and effectively becomes a factory. This is similar to #171 but specific to just extensions.

If we support this for interop, we may not want to support it without interop as I'm not sure this is really preferable to an explicit (and single) factory.

@DependencyGraph
interface ParentGraph : ChildGraphProvider {
  fun createChild(@Provides input: String): ChildGraph
}

@GraphExtension
interface ChildGraph {
  // No factory defined here
}

Alternatives/workarounds

Use a traditional GraphExtension.Factory

@DependencyGraph
interface ParentGraph : ChildGraph.Factory {
  
}

@GraphExtension
interface ChildGraph {
  // Define a factory
  @GraphExtension.Factory
  interface Factory {
    fun createChild(@Provides input: String): ChildGraph
  }
}

[consp1racy]

First code sample misses the ChildGraphProvider type. In practice there would always be such factory type, but perhaps without the forgotten @Subcoponent.Factory annotation.

Not supporting this presents an opportunity to make the code explicit during migration to Metro. That's going to result in improved readability (good for AI).

[ZacSweers]

"good for AI" is not a motivating reason for anything in this project, fyi.