[LL FIR] rename testdata to testData to avoid copyright generation

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/fileStructure/propertyAccessorsScript.kts

@@ -0,0 +1,13 @@
+/* RootScriptStructureElement */var x: Int = 10/* DeclarationStructureElement */
+    get() = field
+    set(value) {
+        field = value
+    }
+
+class X {/* ClassDeclarationStructureElement */
+    var y: Int = 10/* DeclarationStructureElement */
+        get() = field
+        set(value) {
+            field = value
+        }
+}