Migrate boxInline tests to new multi-file framework

compiler/testData/codegen/boxInline/simple/extensionLambda.kt

@@ -0,0 +1,17 @@
+// FILE: 1.kt
+
+package test
+
+inline fun <T> String.test(default: T, cb: String.(T) -> T): T = cb(default)
+
+// FILE: 2.kt
+
+import test.*
+
+fun box(): String {
+    val p = "".test(50.0) {
+        it
+    }
+
+    return if (p == 50.0) "OK" else "fail $p"
+}