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

test/javascripts/components/d-icon-test.js.es6

@@ -9,7 +9,10 @@ componentTest("default", {
     const html = this.$()
       .html()
       .trim();
-    assert.equal(html, '<i class="fa fa-bars d-icon d-icon-bars"></i>');
+    assert.equal(
+      html,
+      '<svg class="fa d-icon d-icon-bars svg-icon svg-string" xmlns="http://www.w3.org/2000/svg"><use xlink:href="#bars"></use></svg>'
+    );
   }
 });
 
@@ -22,7 +25,7 @@ componentTest("with replacement", {
       .trim();
     assert.equal(
       html,
-      '<i class="fa fa-exclamation-circle d-icon d-icon-d-watching"></i>'
+      '<svg class="fa d-icon d-icon-d-watching svg-icon svg-string" xmlns="http://www.w3.org/2000/svg"><use xlink:href="#exclamation-circle"></use></svg>'
     );
   }
 });