Only focus first element of dropdown menus if using keyboard (#8679)

* Only focus first item of dropdown if it was opened via keyboard

* Improve keyboard VS mouse navigation of dropdown menus

app/javascript/mastodon/actions/dropdown_menu.js

@@ -1,8 +1,8 @@
 export const DROPDOWN_MENU_OPEN = 'DROPDOWN_MENU_OPEN';
 export const DROPDOWN_MENU_CLOSE = 'DROPDOWN_MENU_CLOSE';
 
-export function openDropdownMenu(id, placement) {
-  return { type: DROPDOWN_MENU_OPEN, id, placement };
+export function openDropdownMenu(id, placement, keyboard) {
+  return { type: DROPDOWN_MENU_OPEN, id, placement, keyboard };
 }
 
 export function closeDropdownMenu(id) {