Auto-focus emoji picker's search field (#8688)

Fixes #6056

app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.js

@@ -261,6 +261,7 @@ class EmojiPickerMenu extends React.PureComponent {
           skin={skinTone}
           showPreview={false}
           backgroundImageFn={backgroundImageFn}
+          autoFocus
           emojiTooltip
         />