This helper is used for extracting part of the issue / MR / whatever
description for use in the description meta tag:
1. To do that, we look at the source of the Markdown description.
2. We then strip out all HTML tags.
3. And then take the first 30 words.
Doing that can be really slow - especially as Markdown is supposed to be
treated as plain text. There are many better ways to do this, but the
immediate performance fix is to swap steps 2 and 3. This does mean that
the description may be less than 30 words (or even empty), but it is
much faster when the description is very long.
A limited number of pages have defined their own descriptions, but
otherwise we default to the Project's description (if `@project` is
set), or the old `brand_title` fallback.
The image will either be the uploaded project icon (never a generated
one), the user's uploaded icon or Gravatar, or, finally, the GitLab
logo.
Sean McGivern