Add PossiblyCurrentContext::make_not_current_as_possibly_current

[mickvangelderen]

Fixes #1704

Allow making the context not current by reference.

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality

[kchibisov]

I feel like in_place is a bit better, since it's just shorter...

Other than that should be good.

[mickvangelderen]

I rebased to redo the commit message after the name-change

[kchibisov]

I completely forgot, could you change the src/lib.rs in examples to also use this function and not Option?

[kchibisov]

Though, it has reasons to use Option since it's needed during drop, so maybe it's fine as is.

Up to you, but I won't block on it, since it won't save much, just by looking more into it.

[mickvangelderen]

I think the example code can be reworked to match the diagram I sketched in #1704. There are a number of Option<T>'s that together define a state machine. One thing I noticed is that it is possible that the renderer will be asked to resize while the application is suspended and the context is not current. I am not sure this is a problem, but the fact that this is not obvious is a result of the current type-level design.

If you are curious what I mean, I'm happy to take a shot at improving the example code and make a proposal. For this PR however, I think this is good enough.

The proposal would look something like this (taken from the engine I'm working on):

#[derive(Default)]
enum EngineState<TGame, TRenderContext: craft_engine_core::RenderContext> {
    #[default]
    Uninitialized,
    Initialized {
        game: TGame,
        render_context: TRenderContext,
        window: winit::window::Window,
    },
    Suspended {
        game: TGame,
        render_context: TRenderContext::Suspended,
    },
    Exited,
}

Except that there would not be a generic game state or render context, and the render context can be inlined.

[kchibisov]

Nah, the only issue is because we need to drop the context from inside the resume without moving it out, which is not possible, since it's all RAII...

Like the example is already quite complex, so I'd probably won't add anthying more to it.