Remove start_app_as_body.

[futursolo]

Description

Fixes #2344

This Pull Request Removes _as_body variant of start_app Due to the following reasons:

1. If body is created repeatedly, it can causes Yew router when pushing history breaks form submits #2344 where event listeners are not re-registered.
2. It works poorly with the upcoming SSR hydration (Hydration makes an assumption that the first element in the root element is aligned to first VTag in the virtual dom.).

Checklist

• I have run cargo make pr-flow
• I have reviewed my own code
• I have added tests

[voidpumpkin]

Could you add a note about this change in migration docs?

[github-actions]

Visit the preview URL for this PR (updated for commit a28a590):

https://yew-rs--pr2346-remove-as-body-h887e32t.web.app

_{(expires Sun, 16 Jan 2022 11:09:45 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

[voidpumpkin]

Well looks good for me but I would like for @siku2 to take a look as well just in case.

[voidpumpkin]

I realized this page is not added to the navigation bar. Could you add it?

[futursolo]

I think the migration guide should remain "hidden" until released, shouldn't it?

(This is the same as the yew-agent 0.1.0 -> 0.2.0 guide, which is hidden.)

[hamza1311]

Showing it would make 0.19 -> next transition easier but it's something we can do later.

[voidpumpkin]

you guys are right

[voidpumpkin]

Been long enough, if anything we can just implement this again in the future

[qieman]

Hey, Is there any alternative to this method? i want to use start_app_as_body to set body css style.

[sam0x17]

Yes, what is the canonical way of doing this now? I need to set an attribute on body for css theme reasons and can't figure out how to do it

[futursolo]

You can use gloo_utils::body().class_list().add_one("your-class").

If you wish to have body classes managed like start_app_as_body, you can use <Helmet /> from bounce.

If you wish to manage global styling, you can also use <Global /> from stylist.