Add ClassDescriptor.getInlineClassRepresentation

This will be used at least in the JVM backend instead of the current
approach where we're loading the primary constructor's first parameter,
which isn't good enough since primary constructor can be private, and
we can't rely on private declarations in case they're declared in
another module.

core/compiler.common/src/org/jetbrains/kotlin/descriptors/InlineClassRepresentation.kt

@@ -0,0 +1,14 @@
+/*
+ * Copyright 2010-2021 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.descriptors
+
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.types.model.SimpleTypeMarker
+
+class InlineClassRepresentation<Type : SimpleTypeMarker>(
+    val underlyingPropertyName: Name,
+    val underlyingType: Type,
+)