[FIR] Extract expect actual matching into separate phase

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/ExpectActualAttributes.kt

@@ -0,0 +1,58 @@
+/*
+ * 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.declarations
+
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
+import org.jetbrains.kotlin.fir.symbols.SymbolInternals
+import org.jetbrains.kotlin.fir.symbols.ensureResolved
+import org.jetbrains.kotlin.resolve.multiplatform.ExpectActualCompatibility
+import java.util.*
+
+private object ExpectForActualAttributeKey : FirDeclarationDataKey()
+private object ActualForExpectAttributeKey : FirDeclarationDataKey()
+
+typealias ExpectForActualData = Map<ExpectActualCompatibility<FirBasedSymbol<*>>, List<FirBasedSymbol<*>>>
+
+@SymbolInternals
+var FirDeclaration.expectForActual: ExpectForActualData? by FirDeclarationDataRegistry.data(ExpectForActualAttributeKey)
+private var FirDeclaration.actualForExpectMap: WeakHashMap<FirSession, FirBasedSymbol<*>>? by FirDeclarationDataRegistry.data(ActualForExpectAttributeKey)
+
+val FirBasedSymbol<*>.expectForActual: ExpectForActualData?
+    get() {
+        ensureResolved(FirResolvePhase.EXPECT_ACTUAL_MATCHING)
+        return fir.expectForActual
+    }
+
+private fun FirDeclaration.getOrCreateActualForExpectMap(): WeakHashMap<FirSession, FirBasedSymbol<*>> {
+    var map = actualForExpectMap
+    if (map != null) return map
+    synchronized(this) {
+        map = actualForExpectMap
+        if (map == null) {
+            map = WeakHashMap()
+            actualForExpectMap = map
+        }
+    }
+    return map!!
+}
+
+@SymbolInternals
+fun FirDeclaration.getActualForExpect(useSiteSession: FirSession): FirBasedSymbol<*>? {
+    return actualForExpectMap?.get(useSiteSession)
+}
+
+fun FirBasedSymbol<*>.getActualForExpect(session: FirSession): FirBasedSymbol<*>? {
+    ensureResolved(FirResolvePhase.EXPECT_ACTUAL_MATCHING)
+    return fir.getActualForExpect(session)
+}
+
+@SymbolInternals
+fun FirDeclaration.setActualForExpect(useSiteSession: FirSession, actualSymbol: FirBasedSymbol<*>) {
+    val map = getOrCreateActualForExpectMap()
+    map[useSiteSession] = actualSymbol
+}
+

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirResolvePhase.kt

@@ -17,6 +17,7 @@ enum class FirResolvePhase(val noProcessor: Boolean = false) {
     ARGUMENTS_OF_ANNOTATIONS,
     CONTRACTS,
     IMPLICIT_TYPES_BODY_RESOLVE,
+    EXPECT_ACTUAL_MATCHING,
     BODY_RESOLVE;
 
     val requiredToLaunch: FirResolvePhase