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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/contextCollector/lambdaArguments.kt

@@ -0,0 +1,11 @@
+fun test() {
+    block("foo") { s ->
+        block(42) { n ->
+            <expr>s.length + n</expr>
+        }
+    }
+}
+
+fun <T> block(obj: T, block: (T) -> Unit) {
+    block(obj)
+}