[ticket/12351] Add loading indicator to links that are missing it.

When you click on the link, the turning circle is missing, so you don't
know whether it is actually doing something or not, until the response is
served.

PHPBB3-12351
[ticket/12211] Do not run attachment file names twice through htmlspecialchars

Upload filenames are already processed via htmlspecialchars in the
type_cast_helper of the new request class. There is no need to run it through
htmlspecialchars() again in the filespec class.

PHPBB3-12211
Merge remote-tracking branch 'VarunAgw/ticket/12351' into develop-ascraeus

* VarunAgw/ticket/12351:
  [ticket/12351] Add loading indicator to links that are missing it.
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12351] Add loading indicator to links that are missing it.
Merge remote-tracking branch 'marc/ticket/12211' into develop-ascraeus

* marc/ticket/12211:
  [ticket/12211] Do not run attachment file names twice through htmlspecialchars
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12211] Do not run attachment file names twice through htmlspecialchars