[IR] Add context receivers test, fix a flattening fields bug

Signed-off-by: Evgeniy.Zhelenskiy <Evgeniy.Zhelenskiy@jetbrains.com>

#KT-1179

compiler/testData/codegen/box/valueClasses/forStatement.kt

@@ -0,0 +1,18 @@
+// https://youtrack.jetbrains.com/issue/KT-52236/Different-modality-in-psi-and-fir
+// CHECK_BYTECODE_LISTING
+// WITH_STDLIB
+// TARGET_BACKEND: JVM_IR
+// WORKS_WHEN_VALUE_CLASS
+// LANGUAGE: +ValueClasses
+
+@JvmInline
+value class DPoint(val x: Double, val y: Double)
+
+fun box(): String {
+    var res = 0.0
+    for (x in listOf(DPoint(1.0, 2.0), DPoint(3.0, 4.0))) {
+        res += x.x + x.y
+    }
+    require(res == 10.0)
+    return "OK"
+}