Fixes TICS violations in wayland_connector.cpp

[DigraJatin]

Closes #4711

What's new?

Resolved TICS violations in mentioned file.

1. reinterpret_cast -> static_cast
2. initialized earlier uninitalized variable eventfd_t ignored{};
3. added overload for WlClient::from to accept const client.

[RAOF]

Thanks for this!

I think this could be simpler (and avoid const_cast<>) by taking a wl_client const* everywhere instead; client.cpp never needs a non-const wl_client, so we can just store wl_client const* and not need the overrides.