Add declarations from serialization plugin to FIR metadata declarations provider.

These declarations should not be visible to users (and therefore are not added to FIR),
but plugin itself can reference them in already compiled serializable classes,
and therefore they should be available in metadata:

- synthetic deserialization constructor
- static write$Self function

See also:
^KT-55885

plugins/kotlinx-serialization/kotlinx-serialization.common/src/org/jetbrains/kotlinx/serialization/compiler/resolve/NamingConventions.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -30,6 +30,7 @@ object SerializationAnnotations {
     val serialNameAnnotationFqName = FqName("kotlinx.serialization.SerialName")
     val requiredAnnotationFqName = FqName("kotlinx.serialization.Required")
     val serialTransientFqName = FqName("kotlinx.serialization.Transient")
+
     // Also implicitly used in kotlin-native.compiler.backend.native/CodeGenerationInfo.kt
     val serialInfoFqName = FqName("kotlinx.serialization.SerialInfo")
     val inheritableSerialInfoFqName = FqName("kotlinx.serialization.InheritableSerialInfo")
@@ -200,7 +201,8 @@ object SerializersClassIds {
     val kSerializerId = ClassId(SerializationPackages.packageFqName, SerialEntityNames.KSERIALIZER_NAME)
     val enumSerializerId = ClassId(SerializationPackages.internalPackageFqName, Name.identifier(SpecialBuiltins.enumSerializer))
     val polymorphicSerializerId = ClassId(SerializationPackages.packageFqName, Name.identifier(SpecialBuiltins.polymorphicSerializer))
-    val referenceArraySerializerId = ClassId(SerializationPackages.internalPackageFqName, Name.identifier(SpecialBuiltins.referenceArraySerializer))
+    val referenceArraySerializerId =
+        ClassId(SerializationPackages.internalPackageFqName, Name.identifier(SpecialBuiltins.referenceArraySerializer))
     val objectSerializerId = ClassId(SerializationPackages.internalPackageFqName, Name.identifier(SpecialBuiltins.objectSerializer))
     val sealedSerializerId = ClassId(SerializationPackages.packageFqName, Name.identifier(SpecialBuiltins.sealedSerializer))
     val contextSerializerId = ClassId(SerializationPackages.packageFqName, Name.identifier(SpecialBuiltins.contextSerializer))
@@ -209,6 +211,14 @@ object SerializersClassIds {
     val setOfSpecialSerializers = setOf(contextSerializerId, polymorphicSerializerId)
 }
 
+object SerializationRuntimeClassIds {
+
+    val descriptorClassId =
+        ClassId(SerializationPackages.descriptorsPackageFqName, Name.identifier(SerialEntityNames.SERIAL_DESCRIPTOR_CLASS))
+    val compositeEncoderClassId =
+        ClassId(SerializationPackages.encodingPackageFqName, Name.identifier(SerialEntityNames.STRUCTURE_ENCODER_CLASS))
+}
+
 fun findStandardKotlinTypeSerializerName(typeName: String?): String? {
     return when (typeName) {
         null -> null