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

We exclude testData pattern from copyright scope

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

@@ -0,0 +1,13 @@
+inline fun <T, R> with(receiver: T, block: T.() -> R): R {/* DeclarationStructureElement */
+    return receiver.block()
+}
+
+inline fun <T, R> T.let(block: (T) -> R): R {/* DeclarationStructureElement */
+    return block(this)
+}
+
+class B {/* ClassDeclarationStructureElement */
+    fun foo(a: Int) = with(a) {
+        toString().let { it }
+    }/* DeclarationStructureElement */
+}