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

We exclude testData pattern from copyright scope

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

@@ -0,0 +1,9 @@
+fun bar(a: Int, b: (Boolean) -> Unit) {/* DeclarationStructureElement */
+
+}
+
+class A {/* ClassDeclarationStructureElement */
+    fun foo(x: String, y: () -> String) {/* DeclarationStructureElement */
+
+    }
+}