Prototype of kotlinx.serialization FIR plugin:

Implement basic non-parameterized case

compiler/fir/tree/src/org/jetbrains/kotlin/fir/extensions/FirExtension.kt

@@ -36,6 +36,7 @@ data class FirExtensionPointName(val name: Name) {
     constructor(name: String) : this(Name.identifier(name))
 }
 
+// todo: KDOC
 abstract class FirDeclarationPredicateRegistrar {
     abstract fun register(vararg predicates: DeclarationPredicate)
     abstract fun register(predicates: Collection<DeclarationPredicate>)

compiler/fir/tree/src/org/jetbrains/kotlin/fir/extensions/predicate/DeclarationPredicate.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.fir.extensions.AnnotationFqn
 
 // -------------------------------------------- Predicates --------------------------------------------
 
+// todo: Missing KDOC
 sealed class DeclarationPredicate {
     abstract val annotations: Set<AnnotationFqn>
     abstract val metaAnnotations: Set<AnnotationFqn>