Restore min-width to popover.

[jasmussen]

This fixes a regression introduced as part of #8756. Basically we removed the min-width so as to let the content itself expand the popover. But alas an empty textfield, like the URL input field, did not expand the popover as it should. We could look at adding the min-width to the URL input field instead, this should expand the popover, but given the fallout this min-width removal has caused already, it's probably good to keep it in place as a baseline.

Screenshot of this being fixed:

[mtias]

Keeping as baseline sounds good to me.

[youknowriad]

LGTM 👍

[jasmussen]

I'm stepping away for a bit, but please feel free to merge when appropriate.

[aduth]

Mmm, the idea of not having a predefined minimum width for a popover seems sensible. Shouldn't the input specify its own minimum width if this is a desired thing?

(To clarify, this is an observation for future improvement, not a blocker on introducing a fix)

[aduth]

We use popovers for tooltips, for example, which shouldn't have a minimum width (and it shouldn't also be their responsible to unset any such minimum width†).

(Runs to check whether tooltips have regressed Is OK)

† Edit: As it is currently:

gutenberg/packages/components/src/tooltip/style.scss

Lines 25 to 27 in b978aa8

	.components-tooltip:not(.is-mobile) .components-popover__content {
	min-width: 0;
	}