Make simple_tag apply conditional_escape() to its output

[Tim Graham]

This is a security hardening to help prevent XSS (and incorrect HTML) for the common use case of simple_tag.

[Tim Graham]

​PR has a test failure.

[Tim Graham <timograham@…>]

In aef2a0e:

Fixed #25018 -- Changed simple_tag to apply conditional_escape() to its output.

This is a security hardening fix to help prevent XSS (and incorrect HTML)
for the common use case of simple_tag.

Thanks to Tim Graham for the review.