Fix [sc-25008] - correct and improve legacy language warnings

[uberbrady]

The legacy language warning was misfiring when a user's language didn't match the APP_LOCALE from .env.

Additionally, we weren't properly warning when the legacy-language came from Settings or from the user themselves. Both of which should be impossible but still probably not a bad idea to warn on it, anyways

Testing

First, I stashed my changes and prove that the bug exists the way I said -
I will set my user to have a language of 'en-US' and set the APP_LOCALE to 'pt-PT'. I got this message:

Your current APP_LOCALE in your .env is set to "pt-PT" and should be updated to be "en-US" in /Users/uberbrady/Documents/grokability/snipe-it/.env. Translations may display unexpectedly until this is updated.

Then, I reapplied my change and reloaded the dashboard. That message then went away.

Next, I changed the APP_LOCALE to be 'en', and my user's locale to be 'es'. I got this:

APP_LOCALE in .env is set to en and should be updated to be en-US
username admin (1) has a language es and should be updated to be en-US

(Note, we didn't have an es->es-MX fallback in-place, so this behavior is expected)

Finally, I blanked out my user's locale setting, and reloaded the dashboard. The messages I got were:

APP_LOCALE in .env is set to en and should be updated to be en-US
App Settings is set to pt and should be updated to be en-US

(Note, we never had a 'pt' language so it didn't select pt-PT as the fallback)

[shortcut-integration]

This pull request has been linked to Shortcut Story #25008: "Legacy Locale" warning misfires in logs when user has different locale than APP_LOCALE.

[what-the-diff]

PR Summary

This Pull Request focuses heavily on improving the way our application handles user language preferences. Summarizing the changes:

• Inclusion of a New Warning Method
  A new warning function, warn_legacy_locale was added to the CheckLocale class. This function only serves to create a warning message if the user's chosen language does not match the legacy version defined in the system.

• Enhanced Language Setting Warnings
  Warnings about language settings will now be more insightful. They will alert users if the language defined in the '.env' file, their own personal language preference, or the application's preferred language, does not match with the legacy language version.

• Removal of Redundant Warning
  To avoid redundancy, an existing warning that related to a mismatch in the APP_LOCALE defined in the '.env' file, was removed.

• Locale Determination
  The locale (i.e., the language) of the application will now be determined using the App::setLocale method, guided by the legacy language version prescribed in the system.

Overall, these changes should make the system more insightful and user-friendly when it comes to handling language preferences.