This implements the new ext-foreign-toplevel-list-v1 protocol [1].
Implemented analog to the zwlr-foreign-toplevel-management-v1 implementation.
The additional _ext_ in the names was added to avoid name collisions.
[1]: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/187
Co-authored-by: Leon Henrik Plickat <leonhenrik.plickat@stud.uni-goettingen.de>