Rich DiscoveryContext API

[raniejade]

The primary usage of this API is for discovering Test classes. Ideally it's an abstraction over platform specific Test discovery mechanisms. In JVM for example it could be backed by classgraph (we already use it in the JVM implementation for SpekRuntime). On Native (and possible JS) due to the lack of runtime reflection it's backed by compile-time generated information (via a compiler plugin but initially hand rolled). With this API we can move SpekRuntime into the common module without the need of having platform specific modules.

interface TestInfo {
    val path: Path
    fun createInstance(): Spek
}

interface DiscoveryContext {
    fun getTests(): List<TestInfo>

    companion object {
        fun builder(): DiscoveryContextBuilder
    }
}

interface DiscoveryContextBuilder {
   fun addClass(cls: KClass<out Spek>, factory: () -> Spek): DiscoveryContextBuilder
   fun build(): DiscoveryContext
}