Rename JSX files with proper .jsx extension (#23733)

app/javascript/mastodon/components/icon.jsx

@@ -0,0 +1,21 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import classNames from 'classnames';
+
+export default class Icon extends React.PureComponent {
+
+  static propTypes = {
+    id: PropTypes.string.isRequired,
+    className: PropTypes.string,
+    fixedWidth: PropTypes.bool,
+  };
+
+  render () {
+    const { id, className, fixedWidth, ...other } = this.props;
+
+    return (
+      <i className={classNames('fa', `fa-${id}`, className, { 'fa-fw': fixedWidth })} {...other} />
+    );
+  }
+
+}