miroil/display_listener_wrapper: Do not store a reference to shared_ptr

[muhammad23012009]

Fixes the reference getting corrupted in QtMir.

Checklist

• Tests added and pass
• Adequate documentation added
• (optional) Added Screenshots or videos

[Copilot]

Pull request overview

This PR fixes a lifetime/ownership bug in the miroil QtMir integration by ensuring DisplayListenerWrapper owns its std::shared_ptr<mir::compositor::DisplayListener> instead of storing a reference to a shared_ptr that can dangle and become corrupted.

Changes:

• Replace the std::shared_ptr<...> const& member with a by-value std::shared_ptr<...> member in DisplayListenerWrapper to make ownership/lifetime safe.

[AlanGriffiths]

I'm curious: how is this class useful? (I agree the shared_ptr& is questionable, but I'd expect QtMir to implement DisplayListener, not call methods on it.)

[muhammad23012009]

I'm curious: how is this class useful? (I agree the shared_ptr& is questionable, but I'd expect QtMir to implement DisplayListener, not call methods on it.)

DisplayListener is implemented by mir::server::shell, which is returned to QtMir as a result of miroil::SetCompositor. As DisplayListener itself is part of the internal API, miroil is used to alleviate that