Add caching to urlize

[Sarah Boyce]

urlize will checks every word for whether it is a url (and then updates the url to be a html link)
We can add some form of caching so that it doesn't repeat the checks on the same "word"

PR: ​https://github.com/django/django/pull/18665

Benchmarks:

Before:

>>> import cProfile
>>> from django.template.defaultfilters import urlize
>>> cProfile.run("urlize('Django. ' * 1_000)")
         61048 function calls (59047 primitive calls) in 0.030 seconds

After:

>>> import cProfile
>>> from django.template.defaultfilters import urlize
>>> cProfile.run("urlize('Django. ' * 1_000)")
         3783 function calls (3702 primitive calls) in 0.005 seconds

PR to add benchmark to django-asv: ​https://github.com/django/django-asv/pull/91