Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/private/kt8095.kt

@@ -0,0 +1,19 @@
+// FILE: 1.kt
+
+package test
+
+class C(private val a : String) {
+    internal inline fun g(x: (s: String) -> Unit) {
+        x(a)
+    }
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun box(): String {
+    var r = "fail"
+    C("OK").g { r = it }
+    return r
+}