Rewrite/Improve Events guide

Also related: #486.

If possible we should look into improving it before the new docs are there. The guide causes too much confusion.

I will try to expand this list every time i see people having issues related to the guide or events.

• It emits events in the setup hook without some kind of condition. (New) users will therefore often encounter timing issues (emitting events before the js side starts to listen to them)
• Usage of unlisten() right after listening to it - idk if it's caused by mindless copy-paste but this was a problem in peoples apps wayyy too often.
• no mention of the need to unlisten in js when something like component unmounting happens.
• no docs on rust to rust communication -> talking about the trigger methods

Start with the Events guide and related issue #486. Review the setup-hook event timing, JavaScript unlisten usage and cleanup, and Rust-to-Rust trigger methods described in the issue. Done means the guide addresses each listed source of confusion and explains the relevant event lifecycle clearly.