[IR] Remove code duplication in IrTypeCheckerContext

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeCheckerContext.kt

@@ -19,28 +19,12 @@ class IrTypeCheckerContext(override val irBuiltIns: IrBuiltIns) : IrTypeSystemCo
     override fun substitutionSupertypePolicy(type: SimpleTypeMarker): SupertypesPolicy.DoCustomTransform {
         require(type is IrSimpleType)
         val parameters = extractTypeParameters((type.classifier as IrClassSymbol).owner).map { it.symbol }
-        val substitution = parameters.zip(type.arguments).toMap()
+        val typeSubstitutor = IrTypeSubstitutor(parameters, type.arguments, irBuiltIns)
+
         return object : SupertypesPolicy.DoCustomTransform() {
             override fun transformType(context: AbstractTypeCheckerContext, type: KotlinTypeMarker): SimpleTypeMarker {
-                require(type is IrSimpleType)
-
-                return substituteArguments(type)
-            }
-
-            private fun substituteArguments(type: IrSimpleType): IrSimpleType {
-                val realArguments = type.arguments.map {
-                    substitute(it)
-                }.toList()
-
-                return IrSimpleTypeImpl(type.classifier, type.hasQuestionMark, realArguments, type.annotations)
-            }
-
-            private fun substitute(type: IrTypeArgument): IrTypeArgument {
-                if (type is IrStarProjection) return type
-
-                val actualType = (type as IrTypeProjection).type as IrSimpleType
-                substitution[actualType.classifier]?.let { return it }
-                return makeTypeProjection(substituteArguments(actualType), type.variance)
+                require(type is IrType)
+                return typeSubstitutor.substitute(type) as IrSimpleType
             }
         }
     }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSubstitutor.kt

@@ -11,13 +11,14 @@ import org.jetbrains.kotlin.ir.types.impl.buildSimpleType
 import org.jetbrains.kotlin.ir.types.impl.makeTypeProjection
 import org.jetbrains.kotlin.ir.types.impl.toBuilder
 import org.jetbrains.kotlin.ir.util.render
+import org.jetbrains.kotlin.types.model.TypeSubstitutorMarker
 
 
 class IrTypeSubstitutor(
     typeParameters: List<IrTypeParameterSymbol>,
     typeArguments: List<IrTypeArgument>,
     private val irBuiltIns: IrBuiltIns
-) {
+): TypeSubstitutorMarker {
     init {
         assert(typeParameters.size == typeArguments.size) {
             "Unexpected number of type arguments: ${typeArguments.size}\n" +