[Bugfix] Drag and drop form for embedded layers

[mind84]

Drag and drop form configuration is not taken into account for the embedded layers.

This is due to the fact that in the readEditionForms method, the layer configuration is read from the "current" project and not from the embedded project.

To fix this, I did something similar to what I did for this PR.

This time I've also add a cache check. I don't know if it's worth it, since in most cases the modified methods are called before the project cache is set. However, if you think the cache-checking is fine, I could add it to the other methods modified in the previous PR.

I've added unit and playwright tests, since this case is not covered yet.

Thanks

Funded by Faunalia

[Gustry]

Thanks for the fix.
I'm adding a backport 3.7 ?

[mind84]

Thanks for the fix. I'm adding a backport 3.7 ?

Yes thank you