Reduce void | undefined only in conjunction with subtype reduction (#42846)

* Reduce void | undefined only in conjunction with subtype reduction

* Accept new baselines

* Add regression test

tests/cases/compiler/voidUndefinedReduction.ts

@@ -0,0 +1,13 @@
+// @strict: true
+
+// Repro from #42786
+
+function isDefined<T>(value: T | undefined | null | void): value is T {
+  return value !== undefined && value !== null;
+}
+
+declare const foo: string | undefined;
+
+if (isDefined(foo)) {
+  console.log(foo.toUpperCase()); 
+}