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

We exclude testData pattern from copyright scope

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

@@ -0,0 +1,3 @@
+class A(val x: Int = 10, val b: String)/* DeclarationStructureElement */ {/* ClassDeclarationStructureElement */
+    constructor(i: Int) : this(x = 1, b = i.toString())/* DeclarationStructureElement */
+}