Export all View results when items_per_page is 0

John Herreñorequested to merge
issue/views_simple_sitemap_export-3437932:3437932-no-items-exported-pager-no-limit into 1.0.x

ViewResultsUrlGenerator: do not set a range on the query when the export display is set to 0 items_per_page. Update functional test to check for this

Closes #3437932

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