🚀 Feature: C++ SDK Generator

### 🔖 Feature description

In short, it is comparative to other code generators, capnp or thrift or ..., which are capable to generate code for variety of languages.

### 🎤 Pitch

One of the discussions in flutter world is about its concurrency model and the need for supporting native threads. In my opinion, it is not that easy to be decided upon and change flutter architecture and design.

We are working on a platform, fronted in flutter and backend completely in C++. There are different configurations which are possible. For example, the backend could be embedded in same device as fronted or isolated and deployed on a commodity or highend hardware. It depends on the scenario. The platform uses its own communication protocol, undeterministic security model, and many other feasures which I think this is not the place to talk about it. However, I do not say it ia not possible to use appwrite in our product, in backend, but it would be much easier to have a code generator for it. The reason we are not going to use appwrite directly in flutter is about its concurrency model, offloading, platform boundaries violation and other factors which are platform specific.

Thank you for your time, efforts and nice product.
Bests

### 👀 Have you spent some time to check if this issue has been raised before?

- [x] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/appwrite/appwrite/blob/HEAD/CODE_OF_CONDUCT.md)

The issue names no files, tests, or entry points. Start by reviewing the existing language generators in the SDK generator repository and how their output is validated. Define the C++ generator's scope, supported SDK surface, and completion criteria before implementation.

Written by the indexing model from the issue text.