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

app/javascript/mastodon/features/compose/components/warning.jsx

@@ -0,0 +1,26 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import Motion from '../../ui/util/optional_motion';
+import spring from 'react-motion/lib/spring';
+
+export default class Warning extends React.PureComponent {
+
+  static propTypes = {
+    message: PropTypes.node.isRequired,
+  };
+
+  render () {
+    const { message } = this.props;
+
+    return (
+      <Motion defaultStyle={{ opacity: 0, scaleX: 0.85, scaleY: 0.75 }} style={{ opacity: spring(1, { damping: 35, stiffness: 400 }), scaleX: spring(1, { damping: 35, stiffness: 400 }), scaleY: spring(1, { damping: 35, stiffness: 400 }) }}>
+        {({ opacity, scaleX, scaleY }) => (
+          <div className='compose-form__warning' style={{ opacity: opacity, transform: `scale(${scaleX}, ${scaleY})` }}>
+            {message}
+          </div>
+        )}
+      </Motion>
+    );
+  }
+
+}