[IR] Add MFVC generation tests

#KT-1179

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

@@ -0,0 +1,26 @@
+// WITH_STDLIB
+// TARGET_BACKEND: JVM_IR
+// WORKS_WHEN_VALUE_CLASS
+// LANGUAGE: +ValueClasses
+
+@JvmInline
+value class DPoint(val x: Double, val y: Double)
+
+class A(var x: DPoint) {
+    init { x = DPoint(2.0, 3.0) }
+}
+
+class B() {
+    var a = DPoint(4.0, 5.0)
+    val b = a
+    init { a = DPoint(6.0, 7.0) }
+    val c = a
+}
+
+fun box(): String {
+    require(A(DPoint(0.0, 1.0)).x == DPoint(2.0, 3.0)) { "No init used" }
+    require(B().a == DPoint(6.0, 7.0)) { "No init used" }
+    require(B().b == DPoint(4.0, 5.0)) { "Wrong init order used" }
+    require(B().c == DPoint(6.0, 7.0)) { "Wrong init order used" }
+    return "OK"
+}