Merge branch 'gfm-source-once' into 'master'

Loads GFM once for per page

## What does this MR do?

Currently the GFM init code is included every time there is a GFM form on the page. This changes that & only includes in once if any number of GFM forms are on the page.

## What are the relevant issue numbers?

#22827

See merge request !6840
Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG

@@ -7,6 +7,7 @@ v 8.12.7
   - Prevent flash alert text from being obscured when container is fluid. !6694
   - Fix JS bug with select2 because of missing `data-field` attribute in select box. !6812
   - Do not alter 'force_remove_source_branch' options on MergeRequest unless specified. !6817
+  - Fix GFM autocomplete setup being called several times. !6840
 
 v 8.12.6
   - Update mailroom to 0.8.1 in Gemfile.lock  !6814

app/views/layouts/application.html.haml

@@ -11,3 +11,4 @@
     = render 'layouts/page', sidebar: sidebar, nav: nav
 
     = yield :scripts_body
+    = render "layouts/init_auto_complete" if @gfm_form

app/views/projects/_zen.html.haml

+- @gfm_form = true
 - supports_slash_commands = local_assigns.fetch(:supports_slash_commands, false)
 .zen-backdrop
   - classes << ' js-gfm-input js-autosize markdown-area'
@@ -7,6 +8,3 @@
     = text_area_tag attr, nil, class: classes, placeholder: placeholder
   %a.zen-control.zen-control-leave.js-zen-leave{ href: "#" }
     = icon('compress')
-
-- content_for :scripts_body do
-  = render "layouts/init_auto_complete" if current_user && (@target_project || @project)