FIR: fix return statement generation for Unit-returning lambdas...

for case then the expected return type is not Unit.
#KT-56747 fixed

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/ResolveUtils.kt

@@ -65,7 +65,7 @@ fun FirAnonymousFunction.addReturnToLastStatementIfNeeded() {
     if (lastStatement is FirReturnExpression) return
 
     val returnType = (body.typeRef as? FirResolvedTypeRef) ?: return
-    if (returnType.isNothing || returnType.isUnit) return
+    if (returnType.isNothing) return
 
     val returnTarget = FirFunctionTarget(null, isLambda = isLambda).also { it.bind(this) }
     val returnExpression = buildReturnExpression {

compiler/testData/debug/localVariables/suspend/mergeLvt.kt

@@ -43,7 +43,11 @@ suspend fun box() {
 // test.kt:16 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int, $this$extensionFun$iv$iv:AtomicInt=AtomicInt, $i$f$extensionFun:int=0:int
 // test.kt:20 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int
 // test.kt:21 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int, $i$a$-suspendCoroutineUninterceptedOrReturn-TestKt$suspendBar$2$iv:int=0:int
+
+// EXPECTATIONS ClassicFrontend JVM JVM_IR
 // test.kt:22 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int, $i$a$-suspendCoroutineUninterceptedOrReturn-TestKt$suspendBar$2$iv:int=0:int
+
+// EXPECTATIONS ClassicFrontend FIR JVM JVM_IR
 // test.kt:20 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int
 // test.kt:23 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null, $i$f$suspendBar:int=0:int
 // test.kt:26 box: $continuation:kotlin.coroutines.Continuation=TestKt$box$1, $result:java.lang.Object=null

compiler/testData/ir/irText/lambdas/lambdaReturningUnit.fir.ir.txt

@@ -11,4 +11,5 @@ FILE fqName:<root> fileName:/lambdaReturningUnit.kt
         block: FUN_EXPR type=kotlin.Function0<kotlin.Any?> origin=LAMBDA
           FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> () returnType:kotlin.Any?
             BLOCK_BODY
-              GET_OBJECT 'CLASS IR_EXTERNAL_DECLARATION_STUB OBJECT name:Unit modality:FINAL visibility:public superTypes:[kotlin.Any]' type=kotlin.Unit
+              RETURN type=kotlin.Nothing from='local final fun <anonymous> (): kotlin.Any? declared in <root>.box'
+                GET_OBJECT 'CLASS IR_EXTERNAL_DECLARATION_STUB OBJECT name:Unit modality:FINAL visibility:public superTypes:[kotlin.Any]' type=kotlin.Unit

compiler/testData/ir/irText/lambdas/lambdaReturningUnit.fir.kt.txt

@@ -4,7 +4,7 @@ inline fun flaf(block: Function0<Any?>) {
 
 suspend fun box() {
   flaf(block = local fun <anonymous>(): Any? {
-    Unit
+    return Unit
   }
 )
 }

js/js.translator/testData/box/expression/function/lambdaReturnValue.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_K2: JS_IR
 // EXPECTED_REACHABLE_NODES: 1285
 
 fun <T> rawReturnValue(fn: () -> T): Any {