Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/31276

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/30637

Adds rel="noopener noreferrer" to all links with target="_blank"

See merge request !2071

The button allows to choose a ".gitlab-ci.yml" template that automatically
sets up the deployment of an application.
The currently supported template is Kubernetes template.

Signed-off-by: NRémy Coutable <remy@rymai.me>

On a merge request with over 1000 changed files, there were redundant
calls to blob_text_viewable?, which incurred about 7% of the time.

Improves #14775

the <pre><code> wrapping is *always* used by the helper, and *never* by
anywhere else, so pull the wrapping into the helper

paired with @stanhu

This commit builds on the groundwork in
ee008e300b1ec0abcc90e6a30816ec0754cea0dd, which refactored the backend
so the same code could be used for new dropdowns. In this commit its
used for templates for the `.gitlab-ci.yml` files.