[FIR] Add utility function for constructing user type ref on the air

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/extensions/RawUserTypeBuilder.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2010-2022 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.
+ */
+
+package org.jetbrains.kotlin.fir.extensions
+
+import org.jetbrains.kotlin.fir.types.FirQualifierPart
+import org.jetbrains.kotlin.fir.types.FirTypeProjection
+import org.jetbrains.kotlin.fir.types.FirUserTypeRef
+import org.jetbrains.kotlin.fir.types.builder.buildUserTypeRef
+import org.jetbrains.kotlin.fir.types.impl.FirQualifierPartImpl
+import org.jetbrains.kotlin.fir.types.impl.FirTypeArgumentListImpl
+import org.jetbrains.kotlin.name.Name
+
+class QualifierPartBuilder(internal val destination: MutableList<FirQualifierPart>) {
+    fun part(name: Name, argumentsBuilder: TypeArgumentsBuilder.() -> Unit = {}) {
+        val typeArgumentList = FirTypeArgumentListImpl(source = null)
+        TypeArgumentsBuilder(typeArgumentList).argumentsBuilder()
+        destination += FirQualifierPartImpl(source = null, name, typeArgumentList)
+    }
+
+    class TypeArgumentsBuilder(internal val typeArgumentList: FirTypeArgumentListImpl) {
+        fun argument(typeArgument: FirTypeProjection) {
+            typeArgumentList.typeArguments += typeArgument
+        }
+    }
+}
+
+fun buildUserTypeFromQualifierParts(
+    isMarkedNullable: Boolean,
+    builder: QualifierPartBuilder.() -> Unit
+): FirUserTypeRef {
+    return buildUserTypeRef {
+        this.isMarkedNullable = isMarkedNullable
+        QualifierPartBuilder(qualifier).builder()
+    }
+}