Improve Component Hook Ergonomics

[VasanthakumarV]

Objective

Fixes: #21794

Solution

• If a hook-path is not provided by the user we insert the default path.

Testing

Added a doctest (Edit).

Ran and looked at the expanded macro of the following example,

use bevy_ecs::lifecycle::HookContext;
use bevy_ecs::prelude::*;
use bevy_ecs::world::DeferredWorld;

#[derive(Component)]
#[component(on_add, on_insert, on_despawn, on_remove=on_remove)]
struct Tile;

impl Tile {
    fn on_add(_world: DeferredWorld, _context: HookContext) {
        println!("added");
    }
    fn on_insert(_world: DeferredWorld, _context: HookContext) {
        println!("inserted");
    }
    fn on_despawn(_world: DeferredWorld, _context: HookContext) {
        println!("despawned");
    }
}

fn on_remove(_world: DeferredWorld, _context: HookContext) {
    println!("removed");
}

fn main() {
    let mut world = World::new();
    let entity = world.spawn(Tile);
    entity.despawn();
}

[alice-i-cecile]

I quite like this change, but it needs doc tests, both to ensure that it keeps working, and to make sure that it's discoverable.

[cart]

Love it!

This has been addressed