Add multiplatform test with substitution, fix deep supertypes

This commit fixes ambiguity problems introduced before
in MPP tests with deep supertypes

#KT-29636 Fixed

idea/testData/fir/multiModule/mppFakeOverrides/common/common.kt

@@ -0,0 +1,10 @@
+expect open class A<T>() {
+    open fun foo(arg: T)
+}
+open class B : A<String>() {
+    // Fake: override fun foo(arg: String) = super.foo(arg)
+    // Fake (JVM only) (?): override fun bar(arg: String): String = super.bar(arg)
+}
+open class C : B() {
+    open fun bar(arg: CharSequence): String = arg.toString()
+}

idea/testData/fir/multiModule/mppFakeOverrides/common/common.txt

@@ -0,0 +1,19 @@
+FILE: common.kt
+    <T> public open expect class A {
+        public constructor(): super<R|kotlin/Any|>()
+
+        public open function foo(arg: R|T|): R|kotlin/Unit|
+
+    }
+    public open class B : R|A<kotlin/String>| {
+        public constructor(): super<R|A<kotlin/String>|>()
+
+    }
+    public open class C : R|B| {
+        public constructor(): super<R|B|>()
+
+        public open function bar(arg: R|kotlin/CharSequence|): R|kotlin/String| {
+            return@@@bar <Unresolved name: arg>#.<Unresolved name: toString>#()
+        }
+
+    }