Add Paginator.get_page() to abstract away pagination boilerplate handling of invalid pages

[Ian Foote]

In the ​documentation for pagination, we recommend using this boilerplate:

try:
    contacts = paginator.page(page)
except PageNotAnInteger:
    # If page is not an integer, deliver first page.
    contacts = paginator.page(1)
except EmptyPage:
    # If page is out of range (e.g. 9999), deliver last page of results.
    contacts = paginator.page(paginator.num_pages)

This could be abstracted away into a simple method on the ​Paginator class, perhaps named something like results_for_page.

[Sami J. Lehtinen]

When I last used the paginator, I needed to copy'n'paste the boilerplate code, so probably could do with an utility method. I'll take a look.

[Sami J. Lehtinen]

​https://github.com/django/django/pull/8305

[Tim Graham <timograham@…>]

In 407c124:

Fixed #28032 -- Added Paginator.get_page().

Moved boilerplate from docs to a method.