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

compiler/testData/script/hello.kts

@@ -0,0 +1,2 @@
+
+print("Hello from basic script!")

compiler/testData/script/hello.req1.kts

@@ -0,0 +1,4 @@
+
+@file:Import("hello_req.kt")
+
+print("Hello from ${RequiredFromHello().name}!")

compiler/testData/script/hello_args.kts

@@ -0,0 +1,2 @@
+
+print("Hello, ${args[0]}!")

compiler/testData/script/hello_req.kt

@@ -0,0 +1,5 @@
+
+class RequiredFromHello {
+
+    val name = "required"
+}