Add Disabled/Enabled state scoped components

[Freyja-moth]

Objective

Fixes #19087

Solution

Add

• DisableWhen
• DisableOnEnter
• DisableOnExit
• EnableWhen
• EnableOnEnter
• EnableOnExit

Testing

This is the exact same code copied over from DespawnWhen/DespawnOnEnter/DespawnOnExit, so it should work. If tests are needed lmk and I'll add them

Showcase

#[derive(Component, Clone, Default)]
pub struct Player;

#[derive(States, Hash, PartialEq, Eq, Clone, Default, Debug)]
pub enum GameState {
    #[default]
    MainMenu,
    Loading,
    InGame
}

fn main() -> AppExit {
    App::new()
        .init_state::<GameState>()
        .add_systems(Startup, player.spawn())
        .run()
}

fn player() -> impl Scene {
    bsn! {
        Disabled
        Player
        EnableOnEnter(GameState::InGame)
        DisableOnExit(GameState::InGame)
    }
}

[alice-i-cecile]

Marked as X-Needs-SME because there's been some controversy around best practices with disabling components, and how effective our existing implementation is (query-matching observers would help a lot).

I'm personally a bit reluctant to promote them further until that situation is improved.

[Freyja-moth]

I understand the issues surrounding entity disabling, however I'm not certain why this pr is blocked on those issues since it doesn't touch on them. Merging this doesn't make fixing any of those issues any harder or easier.

This is something I do need in order to refactor jackdaws ui and having to wait an entire release cycle to do so because of issues not affected by this pr is quite frustrating.

[alice-i-cecile]

The argument here is "attractive nuisance" and "this would make it harder to remove entity disabling because it breaks more users". I see your point though.

[alice-i-cecile]

This is correctly implemented and useful. I'm going to approve and merge this, in the hopes that it will be an impetus for improving the underlying functionality.