[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/Elvis.fir.kt

@@ -0,0 +1,9 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    bar(x ?: 0)
+    if (x != null) bar(x ?: x)
+    bar(x)
+}