Introduce ui.teleport element

[CrystalWindSnake]

This PR introduces a ui.teleport component to NiceGUI, mirroring the functionality of Vue's Teleport. It is the key for enabling the direct creation of any NiceGUI component within table cell slots(#3148).

[falkoschindler]

Thanks a lot for this pull request, @CrystalWindSnake! The teleport element feels pretty magical!

Here are some thoughts about it:

• The target container is specified using a CSS select. I guess this is helpful when addressing an HTML element like in the demo. But sometimes you might want to use a NiceGUI element like in the pytests. Could we support both, CSS strings and references to a UI element?

• The force_update method feels a bit like the existing update method. Do you think we could simply re-use update()? Otherwise I fear users will call update() and wonder why the content doesn't appear in the target container.

• You added the ui.teleport element to the documentation section about control element. I'd suggest to move it to the section about page layout, since it isn't limited to control elements and it is basically a very powerful layouting feature.

• I noticed that the teleported content in disappears when reloading the page. This is ok on individual pages, but confusing on the auto-index page. Do you think there's anything we can do about that?

[CrystalWindSnake]

@falkoschindler Thank you for your help.

• we should be able to construct appropriate CSS selectors using element.id.
• force_update() is used in scenarios where the target container is destroyed and rebuilt, which might be different from the scenarios for update().Additionally, force_update forces a re-render of teleport by updating the key, but I don't understand how this differs from props updates. I'm concerned it might cause other issues . However, I respect your decision and defer to your judgment .
• Agreed. it is more appropriate to classify the ui.teleport component as a layout element.
• I found a solution from the Vue repository, but I don't understand the reason behind it. The issue is indeed resolved.

[falkoschindler]

Thanks again, @CrystalWindSnake!
Looks like the PR is ready to merge. 🚀