K2 Scripting: enable script diagnostic tests for FIR

also add script scopes test

compiler/testData/diagnostics/tests/script/topLevelVariable.fir.kts

@@ -0,0 +1,20 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+import kotlin.reflect.KProperty
+
+class Delegate {
+    operator fun getValue(t: Any?, p: KProperty<*>): Int {
+        return 1
+    }
+}
+
+val a: Int by <!DELEGATE_SPECIAL_FUNCTION_MISSING!>Delegate()<!>
+
+class Foo {
+    val a: Int by <!DELEGATE_SPECIAL_FUNCTION_MISSING!>Delegate()<!>
+}
+
+fun foo() {
+    val a: Int by <!DELEGATE_SPECIAL_FUNCTION_MISSING!>Delegate()<!>
+}
+