Migrate boxMultiFile and boxMultifileClass tests to new multi-file tests

AbstractCompileKotlinAgainstMultifileKotlinTest is broken in this commit; will
be fixed later

compiler/testData/codegen/boxMultiFile/protectedFromLambda.kt

@@ -0,0 +1,27 @@
+// FILE: A.kt
+
+package first
+
+open class A {
+    protected open fun test(): String = "FAIL (A)"
+}
+
+fun box() = second.C().value()
+
+// FILE: B.kt
+
+// See also KT-8344: INVOKESPECIAL instead of INVOKEVIRTUAL in accessor
+
+package second
+
+import first.A
+
+public abstract class B(): A() {
+    val value = {
+        test()
+    }
+}
+
+class C: B() {
+    override fun test() = "OK"
+}