Upgrade to FontAwesome 5 (take two) (#6673)

* Add missing icons to set

* Revert FA5 revert

 This reverts commit 42572ff

* use new SVG syntax in locales

* Noscript page changes (remove login button, center "powered by" footer text)

* Cast wider net for SVG icons in settings

- include any _icon setting for SVG registry (offers better support for plugin settings)

- let themes store multiple pipe-delimited icons in a setting

- also replaces broken onebox image icon with SVG reference in cooked post processor

* interpolate icons in locales

* Fix composer whisper icon alignment

* Add support for stacked icons

* SECURITY: enforce hostname to match discourse hostname

This ensures that the hostname rails uses for various helpers always matches
the Discourse hostname

* load SVG sprite with pre-initializers

* FIX: enable caching on SVG sprites

* PERF: use JSONP for SVG sprites so they are served from CDN

This avoids needing to deal with CORS for loading of the SVG

Note, added the svg- prefix to the filename so we can quickly tell in
dev tools what the file is

* Add missing SVG sprite JSONP script to CSP

* Upgrade to FA 5.5.0

* Add support for all FA4.7 icons

- adds complete frontend and backend for renamed FA4.7 icons

- improves performance of SvgSprite.bundle and SvgSprite.all_icons

* Fix group avatar flair preview

- adds an endpoint at /svg-sprites/search/:keyword

- adds frontend ajax call that pulls icon in avatar flair preview even when it is not in subset

* Remove FA 4.7 font files

lib/cooked_post_processor.rb

@@ -109,7 +109,7 @@ class CookedPostProcessor
 
     span = create_span_node("url", url)
     a.add_child(span)
-    span.add_previous_sibling(create_icon_node("image"))
+    span.add_previous_sibling(create_icon_node("far-image"))
     span.add_next_sibling(create_span_node("help", I18n.t("upload.placeholders.too_large", max_size_kb: SiteSetting.max_image_size_kb)))
 
     # Only if the image is already linked
@@ -137,8 +137,9 @@ class CookedPostProcessor
 
   def add_broken_image_placeholder!(img)
     img.name = "span"
-    img.set_attribute("class", "broken-image fa fa-chain-broken")
+    img.set_attribute("class", "broken-image")
     img.set_attribute("title", I18n.t("post.image_placeholder.broken"))
+    img << "<svg class=\"fa d-icon d-icon-unlink svg-icon\" aria-hidden=\"true\"><use xlink:href=\"#unlink\"></use></svg>"
     img.remove_attribute("src")
     img.remove_attribute("width")
     img.remove_attribute("height")
@@ -407,7 +408,10 @@ class CookedPostProcessor
   end
 
   def create_icon_node(klass)
-    create_node("i", "fa fa-fw fa-#{klass}")
+    icon = create_node("svg", "fa d-icon d-icon-#{klass} svg-icon")
+    icon.set_attribute("aria-hidden", "true")
+    icon << "<use xlink:href=\"##{klass}\"></use>"
+
   end
 
   def create_link_node(klass, url, external = false)