fix: Fix Menu scroll jump

[diegohaz]

Closes #751

Updated the popover state to update the popper styles in the main phase so they're defined before the menu popover receives focus. I'm still not sure if this is the right solution nor the side effects it could have. I need to read Popper.js docs more carefully.

How to test?

Follow the reproduction steps on #751 on https://deploy-preview-801--reakit.netlify.app/

Does this PR introduce breaking changes?

No

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit f7b47f8:

Sandbox	Source
Reakit	Configuration

[github-actions]

Size Change: +258 B (0%)

Total Size: 257 kB

Filename	Size	Change
packages/reakit-playground/dist/reakit-playground.min.js	187 kB	+40 B (0%)
packages/reakit-system/dist/reakit-system.min.js	2.48 kB	+27 B (1%)
packages/reakit-utils/dist/reakit-utils.min.js	3.46 kB	+73 B (2%)
packages/reakit/dist/reakit.min.js	35.9 kB	+118 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
packages/reakit-system-bootstrap/dist/reakit-system-bootstrap.min.js	19.1 kB	0 B
packages/reakit-system-palette/dist/reakit-system-palette.min.js	8.85 kB	0 B

_{compressed-size-action}

[ariakit-bot]

✔️ Deploy preview for reakit ready!

🔨 Explore the source changes: f7b47f8

🔍 Inspect the deploy logs: https://app.netlify.com/sites/reakit/deploys/5fcae621588c180008ab063d

😎 Browse the preview: https://deploy-preview-801--reakit.netlify.app

[codecov]

Codecov Report

Merging #801 (f7b47f8) into master (f302cad) will decrease coverage by 0.08%.
The diff coverage is 36.36%.

@@            Coverage Diff             @@
##           master     #801      +/-   ##
==========================================
- Coverage   95.44%   95.36%   -0.09%     
==========================================
  Files         229      230       +1     
  Lines        3494     3497       +3     
  Branches      950      953       +3     
==========================================
  Hits         3335     3335              
- Misses        158      161       +3     
  Partials        1        1              

Impacted Files	Coverage Δ
packages/reakit/src/Tabbable/Tabbable.ts	92.85% <ø> (-0.30%)	⬇️
packages/reakit/src/Popover/PopoverState.ts	71.42% <36.36%> (-4.05%)	⬇️
...eakit/src/Dialog/__examples__/ChatDialog/index.tsx	100.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f302cad...f7b47f8. Read the comment docs.