Maintain app_mime_list under OpenURIRequestData instead of global

This patch solves multiple requests handling of OpenURI Requests
efficiently as the app_mime_list structure is maintained per request.

Apertis: https://phabricator.apertis.org/T3704



Signed-off-by: Rohan Madgula <Rohan.Madgula@in.bosch.com>
Reviewed-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Differential Revision: https://phabricator.apertis.org/D6184