fix: Fix CalendarView selecting next day due to not respecting current time zone

src/Uno.UI.Tests/Windows_Globalization/When_Calendar.cs

@@ -13,6 +13,22 @@ namespace Uno.UI.Tests.Windows_Globalization
 	[TestClass]
 	public class When_Calendar
 	{
+		[TestMethod]
+		public void When_DateTimeOffset_Is_Next_Day_If_Converted_To_Utc()
+		{
+			var calendar = new WG.Calendar();
+			var offset = new DateTimeOffset(year: 2023, month: 5, day: 1, hour: 21, minute: 0, second: 0, TimeSpan.FromHours(-5));
+			calendar.SetDateTime(offset);
+			// calendar.Day must be 1 here to match WinUI, **and also** not break CalendarView selection of "Today"
+			Assert.AreEqual(1, calendar.Day);
+			Assert.AreEqual(2, offset.UtcDateTime.Day);
+
+			var comparer = new DirectUI.DateComparer();
+			comparer.SetCalendarForComparison(calendar);
+			var result = comparer.CompareDay(offset, new DateTimeOffset(year: 2023, month: 5, day: 1, hour: 4, minute: 0, second: 0, TimeSpan.FromHours(0)));
+			Assert.AreEqual(0, result);
+		}
+
 		[TestMethod]
 		public void When_Gregorian_FixedDate()
 		{

src/Uno.UI/DirectUI/DateComparer.cs

@@ -103,10 +103,7 @@ namespace DirectUI
 
 			global::System.Diagnostics.Debug.Assert(m_spCalendar is { });
 
-			lhs = lhs.ToUniversalTime(); // UNO
-			rhs = rhs.ToUniversalTime(); // UNO
-
-			long delta = lhs.Ticks - rhs.Ticks;
+			long delta = lhs.ToUniversalTime().Ticks - rhs.ToUniversalTime().Ticks;
 			if (delta < 0)
 			{
 				delta = -delta;

src/Uno.UWP/Globalization/Calendar.cs

@@ -190,28 +190,28 @@ namespace Windows.Globalization
 		#region Read / Write _time
 		public int Era
 		{
-			get => _calendar.GetEra(_time.UtcDateTime);
+			get => _calendar.GetEra(_time.DateTime);
 			[NotImplemented]
 			set => global::Windows.Foundation.Metadata.ApiInformation.TryRaiseNotImplemented("Windows.Globalization.Calendar", "int Calendar.Era");
 		}
 
 		public int Year
 		{
-			get => _calendar.GetYear(_time.UtcDateTime);
+			get => _calendar.GetYear(_time.DateTime);
 			set => AddYears(value - Year);
 		}
 
 		public int Month
 		{
-			get => _calendar.GetMonth(_time.UtcDateTime);
+			get => _calendar.GetMonth(_time.DateTime);
 			set => AddMonths(value - Month);
 		}
 
-		public global::Windows.Globalization.DayOfWeek DayOfWeek => (global::Windows.Globalization.DayOfWeek)_calendar.GetDayOfWeek(_time.UtcDateTime);
+		public global::Windows.Globalization.DayOfWeek DayOfWeek => (global::Windows.Globalization.DayOfWeek)_calendar.GetDayOfWeek(_time.DateTime);
 
 		public int Day
 		{
-			get => _calendar.GetDayOfMonth(_time.UtcDateTime);
+			get => _calendar.GetDayOfMonth(_time.DateTime);
 			set => AddDays(value - Day);
 		}
 
@@ -219,7 +219,7 @@ namespace Windows.Globalization
 		{
 			get
 			{
-				var hour = _calendar.GetHour(_time.UtcDateTime);
+				var hour = _calendar.GetHour(_time.DateTime);
 
 				if (hour < 12 || _clock == ClockIdentifiers.TwentyFourHour)
 				{
@@ -236,13 +236,13 @@ namespace Windows.Globalization
 
 		public int Minute
 		{
-			get => _calendar.GetMinute(_time.UtcDateTime);
+			get => _calendar.GetMinute(_time.DateTime);
 			set => AddMinutes(value - Minute);
 		}
 
 		public int Second
 		{
-			get => _calendar.GetSecond(_time.UtcDateTime);
+			get => _calendar.GetSecond(_time.DateTime);
 			set => AddSeconds(value - Second);
 		}
 
@@ -281,7 +281,7 @@ namespace Windows.Globalization
 
 		public int Nanosecond
 		{
-			get => (int)(_calendar.GetMilliseconds(_time.UtcDateTime) * 1000);
+			get => (int)(_calendar.GetMilliseconds(_time.DateTime) * 1000);
 			set => AddNanoseconds(value - Nanosecond);
 		}