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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/fileStructure/propertyWithSetter.kt

@@ -0,0 +1,14 @@
+abstract class Foo {/* ClassDeclarationStructureElement */
+    abstract var id: Int/* DeclarationStructureElement */
+        protected set
+}
+
+class Bar : Foo() {/* ClassDeclarationStructureElement */
+    override var id: Int = 1/* DeclarationStructureElement */
+    public set
+}
+
+fun test() {/* DeclarationStructureElement */
+    val bar = Bar()
+    bar.id = 1
+}