Implement simple "add to compilation" functionality for scripts

(incomplete import - scripts added to the compilation but not yet
imported into scope)
Base functionality needed for #KT-27960

libraries/scripting/jvm-host/testData/importTest/requiredSrc.kt

@@ -0,0 +1,5 @@
+
+class RequiredClass {
+
+    val value = "required"
+}