Allow document to be user scalable for the sake of a11y

[andyra]

Removes user-scalable=no from the viewport meta, which will allow people to scale as needed.

This was originally added in #1613 as a way to ensure that the screen doesn't zoom automatically in mobile Safari when text input sizes are < 16px. The aforementioned PR also forces the text size to be 16px on mobile Safari, though, so the user-scalable attribute is redundant and safe to remove.

https://app.fizzy.do/5986089/cards/3487

[jzimdars]

Let's get @adjogima's take on this. Historically we've set user-scalable-no for webviews in our native apps because scaling is undesirable.

I'd say that's true for PWAs, too. I know accessibility experts and tools all hate when you do this but the user experience of being able to pinch/zoom inside of an app isn't great and breaks the illusion of native in our hybrid apps.

[adjogima]

I'd say ideally we allow zooming on the web but don't in the native app's webviews and maybe PWAs.

If we don't allow zooming at all, one thing that would mitigate is allow zooming on images. On mobile it's often useless to expand images because it doesn't make them any bigger 👇

---

Whatever we do, I think we should try to support the OS' dynamic type size setting.
Now on iOS the only thing I've found is using -apple-system-xxx
For example, setting font: -apple-system-body on the body picks it up 👇

System text size setting	Production	Using font: -apple-system-body on the body

Maybe that's a case for something like

@layer platform {
  [data-platform~=mobile] {
    font: -apple-system-body;
  }
}