WP_List_Table table headers are missing `aria-sort` property for accessibility

[dannylonglegs]

An aria-sort property should be added to table headers to inform the screen reader user whether the columns or rows in a grid can be sorted.

Link to code:
​https://github.com/WordPress/WordPress/blob/700f891c36df5390cff668e876b07fd20cca8af6/wp-admin/includes/class-wp-list-table.php#L1137

[afercia]

@dannylonglegs thanks for your report! This issue is already tracked in #32170. You're very welcome to join and follow the conversation there. Any contribution to help that ticket move on would be greatly appreciated :)