veb: fix generic field access from alias

[felipensp]

Fix #25215

[huly-for-github]

Connected to Huly®: V_0.6-24845

[spytheman]

I think, that cgen should have produced instead of this:

        controllers_sorted = array_clone_to_depth(&global_app->controllers, 0);

something like:

        controllers_sorted = array_clone_to_depth(&global_app->Controller.controllers, 0);

but it did not, because of the alias.

i.e. the proper fix would be to change cgen, to allow for an alias to a struct with embeds.

You can test with:

import veb

pub struct Context {
        veb.Context
}

pub struct App {
        veb.Middleware[Context]
        veb.Controller
        veb.StaticHandler
}

fn main() {
        port := 9008
        mut app := &App{}
        veb.run[App, Context](mut app, port)
}

(which does not use aliases), compared with the code from the issue