[FIR] Introduce ConeFunctionalTypeKind as a replacement of FunctionClassKind

This is needed to provide an ability to extend different kinds of
  functional types

Also, cleanup and rename utilities related to functional types to avoid
  possible confusions

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/FirElementSerializer.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.fir.serialization
 
 import org.jetbrains.kotlin.builtins.StandardNames
+import org.jetbrains.kotlin.builtins.functions.FunctionalTypeKind
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.ClassKind
@@ -681,7 +682,7 @@ class FirElementSerializer private constructor(
                 return lowerBound
             }
             is ConeClassLikeType -> {
-                if (type.isSuspendFunctionType(session)) {
+                if (type.functionalTypeKind(session) == FunctionalTypeKind.SuspendFunction) {
                     val runtimeFunctionType = type.suspendFunctionTypeToFunctionTypeWithContinuation(
                         session, StandardClassIds.Continuation
                     )

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/serializationUtil.kt

@@ -5,11 +5,14 @@
 
 package org.jetbrains.kotlin.fir.serialization
 
+import org.jetbrains.kotlin.builtins.functions.FunctionClassKind
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.diagnostics.ConeIntermediateDiagnostic
 import org.jetbrains.kotlin.fir.languageVersionSettings
-import org.jetbrains.kotlin.fir.types.ConeErrorType
-import org.jetbrains.kotlin.fir.types.typeContext
+import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
+import org.jetbrains.kotlin.fir.types.*
+import org.jetbrains.kotlin.fir.types.impl.ConeClassLikeTypeImpl
+import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.types.AbstractTypeApproximator
 import org.jetbrains.kotlin.types.model.SimpleTypeMarker
 
@@ -21,3 +24,22 @@ class TypeApproximatorForMetadataSerializer(session: FirSession) :
     }
 }
 
+fun ConeKotlinType.suspendFunctionTypeToFunctionTypeWithContinuation(session: FirSession, continuationClassId: ClassId): ConeClassLikeType {
+    require(this.isSuspendFunctionType(session))
+    val kind =
+        if (isReflectFunctionalType(session)) FunctionClassKind.KFunction
+        else FunctionClassKind.Function
+    val fullyExpandedType = type.fullyExpandedType(session)
+    val typeArguments = fullyExpandedType.typeArguments
+    val functionalTypeId = ClassId(kind.packageFqName, kind.numberedClassName(typeArguments.size))
+    val lastTypeArgument = typeArguments.last()
+    return ConeClassLikeTypeImpl(
+        functionalTypeId.toLookupTag(),
+        typeArguments = (typeArguments.dropLast(1) + continuationClassId.toLookupTag().constructClassType(
+            arrayOf(lastTypeArgument),
+            isNullable = false
+        ) + lastTypeArgument).toTypedArray(),
+        isNullable = fullyExpandedType.isNullable,
+        attributes = fullyExpandedType.attributes
+    )
+}