Add default case to facebook::react::displayModeToInt() (#48711)

Summary:
In the `displayModeToInt()` function, there is no default case defined which is causing the following warning in React Native Windows when trying to build on the New Architecture:
```
##[error]node_modules\react-native\ReactCommon\react\renderer\uimanager\primitives.h(163,1): Error C2220: the following warning is treated as an error
D:\a\_work\1\s\node_modules\react-native\ReactCommon\react\renderer\uimanager\primitives.h(163,1): error C2220: the following warning is treated as an error [D:\a\_work\1\s\vnext\Microsoft.ReactNative\Microsoft.ReactNative.vcxproj]
##[warning]node_modules\react-native\ReactCommon\react\renderer\uimanager\primitives.h(163,1): Warning C4715: 'facebook::react::displayModeToInt': not all control paths return a value
D:\a\_work\1\s\node_modules\react-native\ReactCommon\react\renderer\uimanager\primitives.h(163,1): warning C4715: 'facebook::react::displayModeToInt': not all control paths return a value [D:\a\_work\1\s\vnext\Microsoft.ReactNative\Microsoft.ReactNative.vcxproj]
```

Adding the default case removes the warning and resolves the issue. Not sure if using the -1 value in this case is appropriate.

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[General] [Fixed] - Add default case to `displayModeToInt()` function

Pull Request resolved: #48711

Test Plan: Tested on React Native Windows New Arch application and was able to build successfully.

Reviewed By: javache

Differential Revision: D68265335

Pulled By: rshest

fbshipit-source-id: 4724a4c7391b9bf651a122f5de227a0c5e0b6212

packages/react-native/ReactCommon/react/renderer/uimanager/primitives.h

@@ -159,6 +159,9 @@ inline static int displayModeToInt(const DisplayMode value) {
       return 2;
     case DisplayMode::Hidden:
       return 3;
+    default:
+      react_native_assert(0 && "displayModeToInt: Invalid DisplayMode");
+      return -1;
   }
 }