is_plugin_added is always true for Self

[kristoff3r]

Bevy version

0.14.0-rc.2

What you did

The following program panics in Bevy 0.14.0-rc.2, but runs successfully in 0.13.2

use bevy::prelude::*;

fn main() {
    let app = App::new().add_plugins(Foo);
}

pub struct Foo;

impl Plugin for Foo {
    fn build(&self, app: &mut App) {
        if app.is_plugin_added::<Self>() {
            panic!()
        }
    }
}

What went wrong

Either the previous behavior should be restored, or we should document it in the migration guide.

Additional information