Event source location tracking

[SpecificProtagonist]

Objective

Fixes #16776

Solution

• reflect &'static Location as an opaque type
  • I've added this to impls/std.rs because other core types are there too. Maybe they should be split out into a core.rs in another PR.
• add source location to EventId (behind the tracking_change_detection feature flag)

Testing

---

Showcase

fn apply_damage_to_health(
    mut dmg_events: EventReader<DealDamage>,
) {
    for (event, event_id) in dmg_events.read_with_id() {
        info!(
            "Applying {} damage, triggered by {}",
            event.amount, event_id.caller
        );
…

2024-12-12T01:21:50.126827Z  INFO event: Applying 9 damage, triggered by examples/ecs/event.rs:47:16

Migration Guide

• If you manually construct a SendEvent, use SendEvent::new()

[aevyrie]

Oooh, nice.

[alice-i-cecile]

Delightful. I hope we can get all of these shipped for 0.16 :D