Refactor Dialog component

[mnigh]

Notes

• use low level components (DialogOverlay, DialogContent) instead of creating our own nested components (Overlay, Content)
• remove footer prop
• add individual props for actions (firstAction?, secondAction?)
• add required dismissible close button that is first focused element in top right-hand corner

[tristan-orourke]

We should account for three actions (roughly cancel, proceed and decline).
But we need to account for edge cases (eg forms).
Maybe makes sense to have our own footer component which accepts the three buttons but can be wrapped in other contexts if necessary.

[esizer]

Closed by #4136