Add `this` context on all supported objects

For instance, let's start with [`SmartPromise`](https://github.com/Byloth/core/blob/2d62bfbe2009023c695023a966689c072c7b9a9d/src/models/promises/smart-promise.ts) making available via `this` the `isPending`, `isFulfilled` and `isRejected` properties.