[Gradle][KPM] Implement IdeFragmentDependency(&Resolver)

This apis are expected to be called reflectively during
Gradle/Ide import of KPM projects.

libraries/tools/kotlin-gradle-plugin/build.gradle.kts

@@ -1,4 +1,5 @@
 import org.jetbrains.dokka.gradle.DokkaTask
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 import org.jetbrains.kotlin.pill.PillExtension
 
 plugins {
@@ -26,6 +27,10 @@ pill {
     variant = PillExtension.Variant.FULL
 }
 
+kotlin.sourceSets.all {
+    languageSettings.optIn("kotlin.RequiresOptIn")
+}
+
 dependencies {
     compileOnly(gradleKotlinDsl())
     api(project(":kotlin-gradle-plugin-api"))