fix: Fix blur/focus events order on Tabbable on Safari and Firefox on MacOS

[diegohaz]

When changing focus between tabbable elements on Safari and Firefox on MacOS, the blur event on the previous active element was being fired after the focus event on the next active element.

This PR waits for the blur event to happen on the active element before focusing the next element.

Does this PR introduce a breaking change?

No

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[ariakit-bot]

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[codecov]

Codecov Report

Merging #658 into master will increase coverage by 0.58%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #658      +/-   ##
==========================================
+ Coverage   95.01%   95.59%   +0.58%     
==========================================
  Files         143      143              
  Lines        2606     2589      -17     
  Branches      742      734       -8     
==========================================
- Hits         2476     2475       -1     
+ Misses        130      114      -16     

Impacted Files	Coverage Δ
packages/reakit/src/Tabbable/Tabbable.ts	92.98% <100.00%> (+20.00%)	⬆️

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