fix(core): window-specific event delivery, closes #3302

[lucasfernog]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

[amrbashir]

nit: It should be is_valid_label() to match assert_valid_label()

[lucasfernog]

Any help testing this would be very welcome. I did some tests using the API example and the multiwindow example and it looks correct, but there might be other use cases that I didn't cover. I'll merge this so it can get more visibility.
Note that you need the next branch @tauri-apps/api package, so you'd need to clone the repo, cd tooling/api && yarn && yarn build && yarn link and yarn link it on your project.

[FabianLars]

I did some tests earlier and it seemed to work well in regard to the linked issue.
I also tried to test for unwanted side effects and didn't find any, but that's something you can't really be a 100% sure about, so take that with a grain of salt.

Edit: So yes, more people doing their own testing is indeed a good idea 🙏

[lucasfernog]

Thanks Fabian. Good thing we still have time to make tests and get feedback from the community (specially until the stable release) to get this working perfectly :P