Prototype support for kotlin-inject

[ZacSweers]

This adds code gen support for @evant's https://github.com/evant/kotlin-inject

Adapting from @joshafeinberg's prior prototyping in https://github.com/joshafeinberg/CircuitKotlinInject

This works by introducing an @MergeCircuitComponent annotation that can be used on a scoped "circuit component" interface that code gen then processes and generates a kotlin-inject-compatible component impl for, aggregating bound UI and presenter factories within the module.

Pros: multiplatform!
Cons: aggregating processor, no cross-module hinting like anvil and hilt do

Example

// Given an existing app component
@Component
abstract class AppComponent {
  // ...
}

// Write a merged circuit component that extends from it
// The generic type is the parent component
// The argument is the scope key
@MergeCircuitComponent(AppScope::class)
abstract class AppScopeCircuitComponent(@Component appComponent: AppComponent) : CircuitComponent

// Usage
val appComponent = AppComponent::class.create()
val circuitComponent = AppScopeCircuitComponent::class.create(appComponent)
val circuit = circuitComponent.newBuilder().build()

Everything else works the same before as far as using @CircuitInject.

TODO

• Docs
• Tests
• API improvements
  • Should we make a separate runtime for the CircuitComponent and new annotations?
  • Can we further abstract the code gen mode specifics from the Circuit processor? Currently we do custom handling for assisted types
• Inexplicable, generated code doesn't seem able to smart-cast data object types to their type when passing it as an assisted param

[ZacSweers]

Thinking it might be better to leave the parent component to the class itself

// Write a merged circuit component that extends from it
// The argument is the scope key
// Primary constructor params are just copied to the generated impl and passed up
@MergeCircuitComponent(AppScope::class)
abstract class AppScopeCircuitComponent(@Component val parent: AppComponent) : CircuitComponent

[ZacSweers]

I'm not sure this has wheels until evant/kotlin-inject#351 is available. I'm also not able to figure out a way to get past this hurdle of deferring generation until kotlin-inject runs 🤔. I suspect there may be a problem with both plugins deferring.