Fixed #15504 - allow nulling/not changing locale in user bulk edit

[snipe]

This fixed #15504, where when an admin was bulk editing a group of users, the locale setting defaulted to the logged in admin's locale. This change makes it so that we do not update the language on save unless something was specifically chosen, and also grants the ability to null out all selected users' locale.

This also adds locale to the list view and makes it sortable and searchable.

[what-the-diff]

PR Summary

• Localization Feature for User Management
  The update includes a new feature that lets you search for users based on their geographical location or 'locale'. This improves user management functionality by tailoring searches to specific regions.

• User Data Modification Enhancement
  The 'BulkUsersController' tool now has the ability to unset the 'locale' value, essentially providing an option to clear user locale data when required.

• Improved Flexibility in User Field Assignments
  Updates to the 'User' model means that the 'locale' variable now supports mass assignments, streamlining workflows that involve setting regional information for multiple users at once.

• Rich Data Table Presentations
  With the revised 'UserPresenter', you'll now see 'locale' as a new column in your data tables. This allows you to not only search and sort by locale but to also choose whether to display this information.

• Advanced User Info Editing Options
  The bulk edit view has been reshaped to include 'locale' selection for enhanced usability. This allows for comprehensive changes across user profiles, including the ability to set the 'locale' field as null for chosen users.