We assume ARIA roles are case insensitive when setting up the role map entry.
In contrast, previously, when falling back to the next valid role due to the criteria for an earlier role not being met, we were using a case sensitive comparison.
This resulted in infinite recursion when an invalid role contained upper case characters because we kept trying to process the ARIA role we were already processing.
To fix this, use a case sensitive comparison here, making it consistent with other ARIA role checks.
Original Revision: https://phabricator.services.mozilla.com/D253617
Differential Revision: https://phabricator.services.mozilla.com/D253753
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