fix(AnchedOverlay): hide overlay while positioning

[dgreif]

As noted in https://github.com/github/primer/issues/240, the updates from #1322 caused the AnchoredOverlay components to start positioning erratically. After further investigation, I found that they were actually being position at the bottom of the page (wherever the Portal is located) and rendered to determine their size before positioning. Because #1322 removed the visibility: hidden style, they were both visible and focusable before actually being positioned. The focus trap would activate, causing the page to scroll to the bottom, and then the position would be calculated from the anchor. This caused the menus in full page apps to be off significantly.

Here I'm bringing back the visibility property on Overlay to allow for temporarily hiding Overlays before positioning. I've tested this in the new Projects Beta and it's working as expected.

I also found a small bug with SelectPanels when they transitioned from a loading: true to loading: false state. Because the FilteredActionList doesn't render the List element until loading is done, the listContainerRef was null when the useFocusZone call was made. We need to ensure useFocusZone re-checks the ref when loading changes, so I added it to the dependencies param.

Closes https://github.com/github/primer/issues/240

Merge checklist

• Added/updated tests
• Added/updated documentation
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[smockle]

Non-blocking: Would it be better to use a CSS variable for this (ref https://www.joshwcomeau.com/css/styled-components/#css-variables)?

I don’t feel strongly, since these styles already read props in other places (e.g. lines 60–62).

[dgreif]

Great catch! After a month with my head out of PRC, this didn't occur to me but is definitely a pattern I want to keep bringing in wherever possible. Fixed in 54d8783

[smockle]

Nice job tracking this down! Left a non-blocking comment above.

Non-blocking: Can we add a test for this? Either automatic, or a tall tale in Storybook for manual testing?

[dgreif]

Added a test with the anchored overlay open, but I'm not sure I can recreate the scroll issues in JSDOM. Added a story as well for manual testing.