This adds a version of `BKE_id_new_nomain` that takes the ID type parameter as
template argument. This allows the function the return the newly created ID with
the correct type, removing the need to use `static_cast` on the call-site.
To make this work, I added a static `id_type` member to every ID struct. This
can also be used to create a similar API for other id management functions in
future patches.
```cpp
// Old
Mesh *mesh = static_cast<Mesh *>(BKE_id_new_nomain(ID_ME, "Mesh"));
// New
Mesh *mesh = BKE_id_new_nomain<Mesh>("Mesh");
```
Pull Request: https://projects.blender.org/blender/blender/pulls/138383
e09ccc9b35