Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/callableReference/topLevelExtension.kt

@@ -0,0 +1,19 @@
+// FILE: 1.kt
+
+package test
+
+inline fun call(p: Int, s: Int.(Int) -> Int): Int {
+    return p.s(p)
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun box() : String {
+    return if (call(10, Int::calc) == 100) "OK" else "fail"
+}
+
+fun Int.calc(p: Int) : Int {
+    return p * this
+}