Fix popovers hide() being called twice

[RasmusKjeldgaard]

Which issue does this PR close?

This PR closes #2180

What is the new behavior?

The hide functionality has been refactored a bit to ensure that the element is in fact showing, before doing hide logic.

Furthermore, the backdropClick listener was removed, because it was not functional, as described in the commit message:

The event listener was not called because dropdowns onBlur event was
always fired first, closing the dropdown including the popover
component. In fact it was only called when clicking inside the dropdown
because onBlur is not fired then - and thus it is useless at this point.

Components using popover (dropdown only right now) should take care of
calling hide() at the appropriate time themselves, e.g. in onBlur.

Does this PR introduce a breaking change?

• Yes
• No

Are there any additional context?

Checklist:

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Review

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When the pull request has been approved it will be automatically merged to stable via automerge.

[RasmusKjeldgaard]

@andershessellund has checked that this works in the target application

[MadsBuchmann]

teeny tiny comment - otherwise lgtm!