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

compiler/testData/diagnostics/tests/Casts.fir.kt

@@ -0,0 +1,23 @@
+// !CHECK_TYPE
+
+fun test() : Unit {
+  var x : Int? = 0
+  var y : Int = 0
+
+  checkSubtype<Int?>(x)
+  checkSubtype<Int>(y)
+  checkSubtype<Int>(x as Int)
+  checkSubtype<Int>(y as Int)
+  checkSubtype<Int?>(x as Int?)
+  checkSubtype<Int?>(y as Int?)
+  checkSubtype<Int?>(x as? Int)
+  checkSubtype<Int?>(y as? Int)
+  checkSubtype<Int?>(x as? Int?)
+  checkSubtype<Int?>(y as? Int?)
+
+  val s = "" as Any
+  ("" as String?)?.length
+  (data@("" as String?))?.length
+  (@MustBeDocumented()( "" as String?))?.length
+  Unit
+}