JetDiagnosticsTest migrated to TestGenerator

- test data files renamed from *.jet to *.kt

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ObjectExpression.kt

@@ -0,0 +1,10 @@
+fun bar(x: Int): Int = x + 1
+
+fun foo() {
+    val x: Int? = null
+
+    val <!UNUSED_VARIABLE!>a<!> = object {
+        fun baz() = bar(if (x == null) 0 else x)
+        fun quux(): Int = if (x == null) <!TYPE_MISMATCH!>x<!> else x
+    }
+}