Fix the "Last" page link in the search results.
Review Request #2189 — Created July 16, 2021 and submitted
Haystack removed a template context variable we used to grab the last page number, for the "Last" page link in the paginator. This change fixes that anchor. It also fixes up the view code to use the modern version of `range()`, to ensure consistency across Python 2.7 and 3.x. Unit tests were added to ensure this doesn't regress in the future. Testing Done: Verified that search results render and include all the right links on Python 2.x and 3.x. Unit tests passed. Reviewed at https://reviews.reviewboard.org/r/11675/