Derive default date/time formats from user profile language

[Copilot]

TableViewDateColumn and TableViewTimeColumn were resolving default formats from the app runtime language (set in Package.appxmanifest), causing users to see formats like MM/dd/yyyy and 12-hour clock even when their Windows language settings specified otherwise.

Changes

• TableViewTimeColumn: Default ClockIdentifier now reads from GlobalizationPreferences.Clocks[0] instead of DateTimeFormatter.LongTime.Clock, with fallback to "24HourClock".
• TableViewDateColumn: Added constructor that resolves the locale-aware short date pattern via new DateTimeFormatter("shortdate", GlobalizationPreferences.Languages).Patterns[0], with fallback to "shortdate".
• TableViewTimeColumnTests: Updated default ClockIdentifier assertion to match new logic.

// Before — app runtime language
ClockIdentifier = DateTimeFormatter.LongTime.Clock;
DateFormat = "shortdate"; // DP default, resolved by WinRT using app language

// After — user profile language
var clocks = GlobalizationPreferences.Clocks;
ClockIdentifier = clocks.Count > 0 ? clocks[0] : "24HourClock";

var languages = GlobalizationPreferences.Languages;
var patterns = languages.Count > 0 ? new DateTimeFormatter("shortdate", languages).Patterns : null;
DateFormat = patterns?.Count > 0 ? patterns[0] : "shortdate";

A German user with de-DE in Windows Settings → Language will now see dd.MM.yyyy and 24-hour times regardless of the app's manifest default language.