Support responsive rich resource types

[robd003]

A lot of widgets have a minimum width or height and if the consumer
tries to scale down a rich content response for a mobile browser by
using an assumed aspect ratio from the height/width it will most likely
cut off part of the content.

[robd003]

I've had problems with my static height widget being resized due to consumers assuming they should use an aspect ratio when displaying our content. If we implement a min & max for width and height then responsive widgets can be displayed without having content cut off or tons of whitespace.

[robd003]

@iamcal Any chance we could discuss this pull request?

[trackleft]

Why not set an aspect ratio instead of a min max width height?
Bootstrap wraps iframes with a div like this https://getbootstrap.com/docs/4.5/utilities/embed/#aspect-ratios
This adds some CSS that does this

.embed-responsive-16by9::before {
    padding-top: 56.25%;
}
.embed-responsive::before {
    display: block;
    content: "";
}

Which can be calculated like shown in this file https://github.com/twbs/bootstrap/blob/c28934cb1871d6b6bd6a866660493a1137de17c6/scss/helpers/_embed.scss