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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFir/destructuring/destructuringDeclaration.kt

@@ -0,0 +1,7 @@
+// LOOK_UP_FOR_ELEMENT_OF_TYPE: org.jetbrains.kotlin.psi.KtDestructuringDeclaration
+
+data class X(val a: Int, val b: Int)
+
+fun main(x: X) {
+    <expr>val (a, b) = x</expr>
+}