When this repo was migrated to TS, we didn't have any source of truth to get REST API definitions from, so we just duplicated typings from the backend and adapted them a little bit to our repo.

https://github.com/RocketChat/Rocket.Chat.ReactNative/tree/develop/app/definitions

Let's refactor that to use this instead https://www.npmjs.com/package/@rocket.chat/rest-typings

I can't emphasize how important this work is and how much it's going to improve our app maintainability and readability.

Some work was done here, but the scope was bigger #5918
Let's focus on this issue first and then we can focus that PR on migrating the SDK.