Fir2Ir: adjust FirBasedSignatureComposer for constructors

Consatructor's name in the signature should be '<init>', not the
name of the constructed class.

compiler/fir/fir2ir/jvm-backend/src/org/jetbrains/kotlin/fir/backend/jvm/FirJvmMangleComputer.kt

@@ -17,13 +17,13 @@ import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.providers.firProvider
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.resolve.toSymbol
+import org.jetbrains.kotlin.fir.signaturer.irName
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeAliasSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
-import org.jetbrains.kotlin.name.SpecialNames
 import org.jetbrains.kotlin.util.capitalizeDecapitalize.toLowerCaseAsciiOnly
 import org.jetbrains.kotlin.utils.addToStdlib.ifNotEmpty
 
@@ -127,7 +127,7 @@ open class FirJvmMangleComputer(
             return
         }
 
-        val name = (this as? FirSimpleFunction)?.name ?: SpecialNames.ANONYMOUS
+        val name = this.irName
         builder.append(name.asString())
 
         platformSpecificSuffix()?.let {

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt

@@ -93,7 +93,7 @@ class FirBasedSignatureComposer(private val mangler: FirMangler) : Fir2IrSignatu
 
                 val classId = containingClassId ?: declaration.containingClass()?.classId
                 val packageName = classId?.packageFqName ?: declaration.symbol.callableId.packageName
-                val callableName = declaration.symbol.callableId.callableName
+                val callableName = declaration.irName
 
                 IdSignature.CommonSignature(
                     packageName.asString(),

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirManglerUtil.kt

@@ -0,0 +1,18 @@
+/*
+ * Copyright 2010-2021 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.signaturer
+
+import org.jetbrains.kotlin.fir.declarations.*
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.name.SpecialNames
+
+val FirCallableDeclaration.irName: Name
+    get() = when (this) {
+        is FirConstructor -> SpecialNames.INIT
+        is FirSimpleFunction -> this.name
+        is FirVariable -> this.name
+        else -> SpecialNames.ANONYMOUS
+    }