Refactor out shared utilities for overlay components

[lavelle]

ModalCurtain already has a couple of these as subcomponents. They could be rewritten to use React Hooks with their own unit tests.

Some code we could share between Modal, Popover and Tooltip

• Esc Listener
• No Scroll
• Focus Trap
• Aria role and label
• Conditional portal-ing
• Popper
• SRR check

[lavelle]

Looking at writing tests for Popover, i definitely think this is a good idea. So many of the tests for ModalCurtain are just for testing the ESC functionality. We can make those generic tests for the utility function, rather than copying them for every component that has that behaviour

cc @danoc

[lavelle]

Started in #351

[lavelle]

Will close this for now. We can maybe handle the other hooks in their own issues if we want to, but i think the most important ones are done.