fix(core): open closed panel on ArrowDown and ArrowUp

[shortcuts]

Summary

With the input focused, pressing ↓ or ↑ should open the panel if it was previously closed.

Result

With openOnFocus: true or a query, and the input focused:

• Pressing ↓ will open the panel with the input focused.
• Pressing ↑ will open the panel with the last element of the list focused.

Reference: w3c aria practices
Closes #584

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[francoischalifour]

Putting "On Hold" because tests are not failing when they should (they're not run correctly).

[francoischalifour]

Nice one!