[IR] Unite inline class and multi-field value class representation

#KT-1179

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

@@ -18,4 +18,4 @@ value class GreaterMFVC(val x: SimpleMFVC, val y: IC, val z: SimpleMFVC)
 
 fun gmfvc(ic: IC, x: GreaterMFVC, ic1: UInt) = smfvc(ic, x.x, 0U) + ic(x.y) + smfvc(IC(0U), x.z, ic1)
 
-fun box() = "todo"
+fun box() = "OK" // todo real test

compiler/testData/diagnostics/tests/inlineClasses/basicInlineClassDeclaration.txt

@@ -44,3 +44,4 @@ public inline object InlineObject {
     public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
 }
+

compiler/testData/diagnostics/tests/valueClasses/basicValueClassDeclaration.txt

@@ -57,3 +57,4 @@ package kotlin {
         }
     }
 }
+