[A11Y] Add aria-label to dropdown toggles (#2668)

Implement custom accessible dropdown toggle labels for forum components

Making the a11y label more specific to the specific action it performs is critical for good UX with assistive technologies.

locale/core.yml

@@ -278,6 +278,7 @@ core:
       rename_button: => core.ref.rename
       reply_button: => core.ref.reply
       restore_button: => core.ref.restore
+      toggle_dropdown_accessible_label: Toggle discussion actions dropdown menu
 
     # These translations are used in the discussion list.
     discussion_list:
@@ -316,10 +317,12 @@ core:
     header:
       admin_button: Administration
       back_to_index_tooltip: Back to Discussion List
+      locale_dropdown_accessible_label: Change forum locale
       log_in_link: => core.ref.log_in
       log_out_button: => core.ref.log_out
       profile_button: Profile
       search_placeholder: Search Forum
+      session_dropdown_accessible_label: Toggle session options dropdown menu
       settings_button: => core.ref.settings
       sign_up_link: => core.ref.sign_up
 
@@ -332,6 +335,7 @@ core:
       meta_title_text: => core.ref.all_discussions
       refresh_tooltip: Refresh
       start_discussion_button: => core.ref.start_a_discussion
+      toggle_sidenav_dropdown_accessible_label: Toggle navigation dropdown menu
 
     # These translations are used by the sorting control above the discussion list.
     index_sort:
@@ -339,6 +343,7 @@ core:
       newest_button: Newest
       oldest_button: Oldest
       relevance_button: Relevance
+      toggle_dropdown_accessible_label: Change discussion list sorting
       top_button: Top
 
     # These translations are used in the Log In modal dialog.
@@ -359,6 +364,7 @@ core:
       mark_all_as_read_tooltip: => core.ref.mark_all_as_read
       mark_as_read_tooltip: Mark as Read
       title: => core.ref.notifications
+      toggle_dropdown_accessible_label: View notifications
       tooltip: => core.ref.notifications
 
     # These translations are used by tooltips displayed for individual posts.
@@ -375,6 +381,7 @@ core:
       edit_button: => core.ref.edit
       hide_confirmation: "Are you sure you want to delete this post?"
       restore_button: => core.ref.restore
+      toggle_dropdown_accessible_label: Toggle post controls dropdown menu
 
     # These translations are used in the scrubber to the right of the post stream.
     post_scrubber:
@@ -448,6 +455,7 @@ core:
       delete_error_message: "Deletion of user <i>{username} ({email})</i> failed"
       delete_success_message: "User <i>{username} ({email})</i> was deleted"
       edit_button: => core.ref.edit
+      toggle_dropdown_accessible_label: Toggle user controls dropdown menu
 
     # These translations are used in the alert that is shown when a new user has not confirmed their email address.
     user_email_confirmation:
@@ -462,6 +470,10 @@ core:
     badge:
       hidden_tooltip: Hidden
 
+    # These translations are used in the dropdown component.
+    dropdown:
+      toggle_dropdown_accessible_label: Toggle dropdown menu
+
     # These translations are displayed as error messages.
     error:
       dependent_extensions_message: "Cannot disable {extension} until the following dependent extensions are disabled: {extensions}"