Provide into_inner() for egui::mutex::{Mutex, RwLock}

[KmolYuan]

Is your feature request related to a problem? Please describe.

Currently, there's no into_inner() method for two lock types egui::mutex::{Mutex, RwLock}.
So the inner value T cannot move out from the wrapper.

/* struct App { */
finish_list: Vec<T>, // Access T without locks
#[serde(skip)]
queue: Vec<Arc<RwLock<T>>>, // Move values to `finish_list` if parallel jobs are done
                            // Also showing some progress bars in GUI

Describe the solution you'd like

Provide fn into_inner(self) -> T through lock_api and atomic_refcell.

Describe alternatives you've considered

• Make the inner value T: Clone, then clone it out.
• Implement serialization (serde) for these locks? It's helpful to save sharable data in the app state.