Support `EntityCommands::trigger` and `EntityWorldMut::trigger`

## What problem does this solve or what need does it fill?

Ergonomics.

## What solution would you like?

```rust
commands.spawn(bundle).trigger(event).insert(bundle2);
```

## What alternative(s) have you considered?

```rust
let id = commands.spawn(bundle).id();
commands.trigger_targets(event, id);
commands.entity(id).insert(bundle2);
```
