fix(widgets): popover components improvements

[Pessimistress]

Change List

• Render popover element inside deck DOM tree (to inherit theming CSS variables and proper removal upon unmount)
• Update popover position on page scrolls, resizes or layout updates

[chrisgervang]

Does this still work for your use case if they're mounted in the deck stack?

[chrisgervang]

I see, body wouldn't have these variables defined unless a stylesheet put them on :root. Everything can be inherited if they stay in the deck stack.

[ibgreen]

A related question that I have been thinking about:

• Would it be possible to specify a "portal" for the popover, so that the popup can take advantage of overlapping any available space in the app outside of the deck canvas. Right now we do this with React.createPortal in apps but one thing that pushes us away from using pure deck widgets for this.
• A portal mode could be useful for any widget that pops up something.

[FatahChan]

when will this be in release?