feat(clerk-js): Add mobile request header back in

Author: chriscanin

packages/expo/src/provider/singleton/createClerkInstance.ts

@@ -165,6 +165,7 @@ export function createClerkInstance(ClerkClass: typeof Clerk) {
         // Instructs the backend that the request is from a mobile device.
         // Some iOS devices have an empty user-agent, so we can't rely on that.
         if (isNative()) {
+          (requestInit.headers as Headers).set('x-mobile', '1');
           (requestInit.headers as Headers).set('x-expo-sdk-version', packageJson.version);
         }
       });