FIR: get rid of FirUnitType in default setters

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/impl/FirDefaultPropertyAccessor.kt

@@ -16,7 +16,7 @@ import org.jetbrains.kotlin.fir.expressions.FirBody
 import org.jetbrains.kotlin.fir.transformInplace
 import org.jetbrains.kotlin.fir.transformSingle
 import org.jetbrains.kotlin.fir.types.FirType
-import org.jetbrains.kotlin.fir.types.impl.FirUnitType
+import org.jetbrains.kotlin.fir.types.impl.FirImplicitUnitType
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 
 abstract class FirDefaultPropertyAccessor(
@@ -57,7 +57,7 @@ class FirDefaultPropertySetter(
 ) : FirDefaultPropertyAccessor(session, psi, isGetter = false) {
     override val valueParameters = mutableListOf(FirDefaultSetterValueParameter(session, psi, propertyType))
 
-    override var returnType: FirType = FirUnitType(session, psi)
+    override var returnType: FirType = FirImplicitUnitType(session, psi)
 
     override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {
         valueParameters.transformInplace(transformer, data)

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/impl/FirBuiltinType.kt

@@ -1,47 +0,0 @@
-/*
- * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.fir.types.impl
-
-import com.intellij.psi.PsiElement
-import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.expressions.FirAnnotationCall
-import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
-import org.jetbrains.kotlin.fir.types.ConeKotlinType
-import org.jetbrains.kotlin.fir.types.ConeKotlinTypeProjection
-import org.jetbrains.kotlin.fir.types.FirResolvedType
-import org.jetbrains.kotlin.name.ClassId
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
-
-sealed class FirBuiltinType(
-    final override val session: FirSession,
-    final override val psi: PsiElement?,
-    val name: String
-) : FirResolvedType {
-    final override val type: ConeKotlinType = ConeClassTypeImpl(
-        FirClassSymbol(
-            ClassId(
-                KOTLIN_PACKAGE_FQ_NAME,
-                Name.identifier(name)
-            )
-        ),
-        ConeKotlinTypeProjection.EMPTY_ARRAY
-    )
-
-    final override val isNullable = false
-
-    final override val annotations: List<FirAnnotationCall>
-        get() = emptyList()
-
-    companion object {
-        private val KOTLIN_PACKAGE_FQ_NAME = FqName.topLevel(Name.identifier("kotlin"))
-    }
-}
-
-class FirUnitType(
-    session: FirSession,
-    psi: PsiElement?
-) : FirBuiltinType(session, psi, "Unit")

compiler/testData/fir/rawBuilder/declarations/simpleClass.txt

@@ -22,7 +22,7 @@ FILE: simpleClass.kt
 
         public? final? lateinit property fau(var): Double
             public? get(): Double
-            public? set(value: Double): R|kotlin/Unit|
+            public? set(value: Double): kotlin.Unit
 
     }
     public? final inline class InlineClass {