[FIR] Extract java class mapping to platform specific component

compiler/fir/jvm/src/org/jetbrains/kotlin/fir/resolve/FirJavaClassMapper.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2020 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.resolve
+
+import org.jetbrains.kotlin.builtins.jvm.JavaToKotlinClassMap
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.declarations.FirClassLikeDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirRegularClass
+
+class FirJavaClassMapper(private val session: FirSession) : FirPlatformClassMapper() {
+    override fun getCorrespondingPlatformClass(declaration: FirClassLikeDeclaration<*>): FirRegularClass? {
+        val javaClassId = JavaToKotlinClassMap.mapKotlinToJava(declaration.symbol.classId.asSingleFqName().toUnsafe())
+        return javaClassId?.let { session.firSymbolProvider.getClassLikeSymbolByFqName(it)?.fir } as? FirRegularClass
+    }
+}
+
+fun FirSession.registerJavaClassMapper() {
+    register(FirPlatformClassMapper::class, FirJavaClassMapper(this))
+}