Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/private/privateClassExtensionLambda.kt

@@ -0,0 +1,35 @@
+// FILE: 1.kt
+
+package test
+
+private class S {
+    fun a(): String {
+        return "K"
+    }
+
+    // This function exposes S which is a private class (package-private in the byte code)
+    // It can be accessed outside the `test` package, which may lead to IllegalAccessError.
+    // This behavior may be changed later
+    internal inline fun call(s: S.() -> String): String {
+        return call2(s)
+    }
+}
+
+@Suppress("PRIVATE_CLASS_MEMBER_FROM_INLINE", "EXPOSED_PARAMETER_TYPE", "EXPOSED_RECEIVER_TYPE")
+internal inline fun S.call2(s: S.() -> String): String {
+    return s() + a()
+}
+
+internal fun call(): String {
+    return S().call {
+        "O"
+    }
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun box(): String {
+    return call()
+}