Fix/simplify invariant for ColorSchemeName, align manual typedef

Summary:
This is a runtime behaviour fix and an API change to `Appearance.setColorScheme`, motivated by a user report where providing `'unspecified'` (valid) to this function would trigger an incorrect invariant throw. Furthermore, there is already a [first party use](https://github.com/facebook/react-native/blob/aec35b896053d9372ccdaf67c939b2eb216d3455/packages/react-native/Libraries/Utilities/Appearance.js#L101) where we call `Appearance.setColorScheme('unspecified')`.

**Changes**

- `Appearance.d.ts` (current public API, manual types): Fix `ColorSchemeName` type to include `'unspecified'` value, and narrow to remove nullability — aligning with existing Flow source for this type in `NativeAppearance`.
- `Appearance.js` (implementation): Fix the invariant throw by **removing it**, and instead narrowing the input type to non-nullable. Redundant work in `getState` and `getColorScheme` is removed.

Changelog: [General][Breaking] `Appearance.setColorScheme` no longer accepts a nullable value

Differential Revision: D80705652

Author: huntie

packages/react-native/Libraries/Utilities/Appearance.d.ts

@@ -9,7 +9,7 @@
 
 import {NativeEventSubscription} from '../EventEmitter/RCTNativeAppEventEmitter';
 
-type ColorSchemeName = 'light' | 'dark' | null | undefined;
+type ColorSchemeName = 'light' | 'dark' | 'unspecified';
 
 export namespace Appearance {
   type AppearancePreferences = {
@@ -34,9 +34,7 @@ export namespace Appearance {
    * appearance of the system UI, only the appearance of the app.
    * Only available on iOS 13+ and Android 10+.
    */
-  export function setColorScheme(
-    scheme: ColorSchemeName | null | undefined,
-  ): void;
+  export function setColorScheme(scheme: ColorSchemeName): void;
 
   /**
    * Add an event handler that is fired when appearance preferences change.

packages/react-native/Libraries/Utilities/Appearance.js

@@ -14,7 +14,6 @@ import typeof INativeAppearance from './NativeAppearance';
 
 import NativeEventEmitter from '../EventEmitter/NativeEventEmitter';
 import EventEmitter from '../vendor/emitter/EventEmitter';
-import invariant from 'invariant';
 
 export type {AppearancePreferences};
 
@@ -60,7 +59,7 @@ function getState(): $NonMaybeType<typeof lazyState> {
       appearanceChanged: [AppearancePreferences],
     }>(NativeAppearance).addListener('appearanceChanged', newAppearance => {
       state.appearance = {
-        colorScheme: toColorScheme(newAppearance.colorScheme),
+        colorScheme: newAppearance.colorScheme,
       };
       eventEmitter.emit('change', state.appearance);
     });
@@ -83,7 +82,7 @@ export function getColorScheme(): ?ColorSchemeName {
       // Lazily initialize `state.appearance`. This should only
       // happen once because we never reassign a null value to it.
       state.appearance = {
-        colorScheme: toColorScheme(NativeAppearance.getColorScheme()),
+        colorScheme: NativeAppearance.getColorScheme(),
       };
     }
     colorScheme = state.appearance.colorScheme;
@@ -94,13 +93,13 @@ export function getColorScheme(): ?ColorSchemeName {
 /**
  * Updates the current color scheme to the supplied value.
  */
-export function setColorScheme(colorScheme: ?ColorSchemeName): void {
+export function setColorScheme(colorScheme: ColorSchemeName): void {
   const state = getState();
   const {NativeAppearance} = state;
   if (NativeAppearance != null) {
-    NativeAppearance.setColorScheme(colorScheme ?? 'unspecified');
+    NativeAppearance.setColorScheme(colorScheme);
     state.appearance = {
-      colorScheme: toColorScheme(NativeAppearance.getColorScheme()),
+      colorScheme,
     };
   }
 }
@@ -114,14 +113,3 @@ export function addChangeListener(
   const {eventEmitter} = getState();
   return eventEmitter.addListener('change', listener);
 }
-
-/**
- * TODO: (hramos) T52919652 Use ?ColorSchemeName once codegen supports union
- */
-function toColorScheme(colorScheme: ?string): ?ColorSchemeName {
-  invariant(
-    colorScheme === 'dark' || colorScheme === 'light' || colorScheme == null,
-    "Unrecognized color scheme. Did you mean 'dark', 'light' or null?",
-  );
-  return colorScheme;
-}

packages/react-native/ReactNativeApi.d.ts

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<b43428758b3aefd30b2bd8a32ec0878a>>
+ * @generated SignedSource<<0170bc4ced1f6d3d4092d837027cd391>>
  *
  * This file was generated by scripts/js-api/build-types/index.js.
  */
@@ -4642,9 +4642,7 @@ declare type Separators = {
   updateProps: (select: "leading" | "trailing", newProps: Object) => void
 }
 declare type sequence = typeof sequence
-declare function setColorScheme(
-  colorScheme: ColorSchemeName | null | undefined,
-): void
+declare function setColorScheme(colorScheme: ColorSchemeName): void
 declare function setComponentProviderInstrumentationHook(
   hook: ComponentProviderInstrumentationHook,
 ): void
@@ -5972,7 +5970,7 @@ export {
   AppState, // f7097b1b
   AppStateEvent, // 80f034c3
   AppStateStatus, // 447e5ef2
-  Appearance, // b23e8105
+  Appearance, // 00cbaa0a
   AutoCapitalize, // c0e857a0
   BackHandler, // a9f9bad9
   BackPressEventName, // 4620fb76