docs(events): Fuller example with pub/sub

[kamranayub]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

==================

Preview

https://kamranayub-docs-events-pubsu.excaliburjs.pages.dev/docs/events#pubsub-or-signal-based-event-bus

Changes

• Add a Shiki Twoslash example implementing custom event handling
• Show how to achieve a pub/sub emitter
• Show how to achieve higher strictness on event name handling
• Clean up existing verbiage and add some more context

Notes

• Inspired by @jyoung4242's post about Signals and Pub/Sub, I noticed our docs lacked info about this use case. When I dug into it, the existing example was not enough to help me create a custom event so I had to look at the engine source.

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[kamranayub]

OK, so if I create my own strict emitter, and override the overloads, it will work:

I could include this example, although it feels like Ex could provide this or support this somehow in an easier way...

[kamranayub]

I'm giving myself credit for Hacktoberfest 🎃

[eonarheim]

@kamranayub Thanks for the add this helps clear it up a ton!