Refactor icons in web UI to use Icon component (#9951)

* Refactor uses of icons to an Icon component in web UI

* Refactor options passed to the Icon component

* Make tests work with absolute component paths

jest.config.js

@@ -22,4 +22,8 @@ module.exports = {
     '!app/javascript/mastodon/test_setup.js',
   ],
   coverageDirectory: '<rootDir>/coverage',
+  moduleDirectories: [
+    '<rootDir>/node_modules',
+    '<rootDir>/app/javascript',
+  ],
 };