Split context for filter bar and unread markers (#16865)

On notifications page, in settings, "Show" for quick filter bar and
unread notifications markers use the same string, while being placed in
the separate contexts - under different settings categories.

This commit splits the contexts, creating new strings:

- "Show filter bar" in place of "Show" for filter bar;

- "Highlight unread notifications" in place of "Show" for unread
  notification markers, which are now simply called "Highlighting";

- There's also "Unread notifications" in place of "Unread notification
  markers" string to accompany the changes to "Show" string under that
  category.

All new strings have new IDs, which will cause previous strings to
invalidate on the next translation update and new strings to be created.
This will help Mastodon translators to know that there are changes and
improve translation in accordance to the source string update.

app/javascript/mastodon/features/notifications/components/column_settings.js

@@ -26,7 +26,8 @@ export default class ColumnSettings extends React.PureComponent {
   render () {
     const { settings, pushSettings, onChange, onClear, alertsEnabled, browserSupport, browserPermission, onRequestNotificationPermission } = this.props;
 
-    const filterShowStr = <FormattedMessage id='notifications.column_settings.filter_bar.show' defaultMessage='Show' />;
+    const unreadMarkersShowStr = <FormattedMessage id='notifications.column_settings.unread_notifications.highlight' defaultMessage='Highlight unread notifications' />;
+    const filterBarShowStr = <FormattedMessage id='notifications.column_settings.filter_bar.show_bar' defaultMessage='Show filter bar' />;
     const filterAdvancedStr = <FormattedMessage id='notifications.column_settings.filter_bar.advanced' defaultMessage='Display all categories' />;
     const alertStr = <FormattedMessage id='notifications.column_settings.alert' defaultMessage='Desktop notifications' />;
     const showStr = <FormattedMessage id='notifications.column_settings.show' defaultMessage='Show in column' />;
@@ -57,11 +58,11 @@ export default class ColumnSettings extends React.PureComponent {
 
         <div role='group' aria-labelledby='notifications-unread-markers'>
           <span id='notifications-unread-markers' className='column-settings__section'>
-            <FormattedMessage id='notifications.column_settings.unread_markers.category' defaultMessage='Unread notification markers' />
+            <FormattedMessage id='notifications.column_settings.unread_notifications.category' defaultMessage='Unread notifications' />
           </span>
 
           <div className='column-settings__row'>
-            <SettingToggle id='unread-notification-markers' prefix='notifications' settings={settings} settingPath={['showUnread']} onChange={onChange} label={filterShowStr} />
+            <SettingToggle id='unread-notification-markers' prefix='notifications' settings={settings} settingPath={['showUnread']} onChange={onChange} label={unreadMarkersShowStr} />
           </div>
         </div>
 
@@ -71,7 +72,7 @@ export default class ColumnSettings extends React.PureComponent {
           </span>
 
           <div className='column-settings__row'>
-            <SettingToggle id='show-filter-bar' prefix='notifications' settings={settings} settingPath={['quickFilter', 'show']} onChange={onChange} label={filterShowStr} />
+            <SettingToggle id='show-filter-bar' prefix='notifications' settings={settings} settingPath={['quickFilter', 'show']} onChange={onChange} label={filterBarShowStr} />
             <SettingToggle id='show-filter-bar' prefix='notifications' settings={settings} settingPath={['quickFilter', 'advanced']} onChange={onChange} label={filterAdvancedStr} />
           </div>
         </div>