ARIA role="combobox" gets a Gecko role of EDITCOMBOBOX.
However, there are two kinds of ARIA comboboxes:
1. ARIA 1.0 comboboxes are contentEditable. Text is entered into the combobox itself.
2. ARIA 1.1 comboboxes are not contentEditable. Instead, they have a textbox child into which text is entered.
On Android, traversal skipped EDITCOMBOBOX Accessibles altogether.
This meant that while 1.1 comboboxes were accessible (because we'd walk inside and land on the textbox), 1.0 comboboxes were not.
We still don't want to land on 1.1 comboboxes because the container isn't useful to the user.
Therefore, only stop on EDITCOMBOBOX Accessibles which are editable.
Differential Revision: https://phabricator.services.mozilla.com/D55224
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extra : moz-landing-system : lando
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