URLField makes Browsable API hides endpoints from openapi schema view

[fao89]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

Have an openapi schema view, with some view using URLField

Expected behavior

See all endpoints on the browsable API

Actual behavior

Endpoints are missing due to HTML comment on regex patterns.

Workflow

Autoschema when mapping URLFields: https://github.com/encode/django-rest-framework/blob/master/rest_framework/schemas/openapi.py#L545-L581 gets the regex pattern from URLValidator which contains <! commenting the HTML from the Browsable API, hiding the following endpoints

[carltongibson]

This is probably #7204. There's an open ticket there to work out exactly how we should map the URL from a URLValidator. Would be great if you wanted to have a think about that.