[FIR] Minor. Add util functions for checks that type is builtin

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/FirTypeUtils.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2010-2019 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.types
+
+import org.jetbrains.kotlin.fir.symbols.StandardClassIds
+import org.jetbrains.kotlin.fir.types.impl.FirImplicitBuiltinTypeRef
+import org.jetbrains.kotlin.name.ClassId
+
+val FirTypeRef.isAny: Boolean get() = isBuiltinType(StandardClassIds.Any, false)
+val FirTypeRef.isNullableAny: Boolean get() = isBuiltinType(StandardClassIds.Any, true)
+val FirTypeRef.isNothing: Boolean get() = isBuiltinType(StandardClassIds.Nothing, false)
+val FirTypeRef.isNullableNothing: Boolean get() = isBuiltinType(StandardClassIds.Nothing, true)
+val FirTypeRef.isUnit: Boolean get() = isBuiltinType(StandardClassIds.Unit, false)
+
+private fun FirTypeRef.isBuiltinType(classId: ClassId, isNullable: Boolean): Boolean =
+    this is FirImplicitBuiltinTypeRef && type.lookupTag.classId == classId && type.isNullable == isNullable

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

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.fir.FirAbstractElement
 import org.jetbrains.kotlin.fir.expressions.FirAnnotationCall
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTagImpl
 import org.jetbrains.kotlin.fir.symbols.StandardClassIds
+import org.jetbrains.kotlin.fir.types.ConeClassLikeType
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.ConeKotlinTypeProjection
 import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
@@ -24,7 +25,7 @@ sealed class FirImplicitBuiltinTypeRef(
     override val annotations: List<FirAnnotationCall>
         get() = emptyList()
 
-    override val type: ConeKotlinType = ConeClassTypeImpl(ConeClassLikeLookupTagImpl(id), typeArguments, isNullable)
+    override val type: ConeClassLikeType = ConeClassTypeImpl(ConeClassLikeLookupTagImpl(id), typeArguments, isNullable)
 }
 
 class FirImplicitUnitTypeRef(