Migrate boxInline tests to new multi-file framework

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

@@ -0,0 +1,22 @@
+// FILE: 1.kt
+
+package test
+
+inline fun <T> doSmth(a: T) : String {
+    return a.toString()
+}
+
+// FILE: 2.kt
+
+import test.*
+
+fun test1(s: Long): String {
+    return doSmth(s)
+}
+
+fun box(): String {
+    val result = test1(11.toLong())
+    if (result != "11") return "fail1: ${result}"
+
+    return "OK"
+}