fix: VisibleBoundsPadding was setting Padding too late.

This was causing some layout problems, specially in TextBlock when the `UseLayoutManager` was activated. It was set on `LayoutUpdated`, which was a little too late.  Setting it on `Loaded` instead fixed the problem.

src/Uno.UI/Behaviors/VisibleBoundsPadding.cs

@@ -145,8 +145,11 @@ internal VisibleBoundsDetails(FrameworkElement owner)
 
 				_visibleBoundsChanged = (s2, e2) => UpdatePadding();
 
-				owner.LayoutUpdated += (s, e) => UpdatePadding();
-				owner.Loaded += (s, e) => ApplicationView.GetForCurrentView().VisibleBoundsChanged += _visibleBoundsChanged;
+				owner.Loaded += (s, e) =>
+				{
+					UpdatePadding();
+					ApplicationView.GetForCurrentView().VisibleBoundsChanged += _visibleBoundsChanged;
+				};
 				owner.Unloaded += (s, e) => ApplicationView.GetForCurrentView().VisibleBoundsChanged -= _visibleBoundsChanged;
 			}
 
@@ -164,6 +167,11 @@ private void UpdatePadding()
 					return;
 				}
 
+				if (!Owner.IsLoaded)
+				{
+					return;
+				}
+
 				Thickness visibilityPadding;
 
 				if (WindowPadding != default(Thickness))
@@ -269,18 +277,9 @@ private Thickness CalculateAppliedPadding(PaddingMask mask, Thickness visibility
 
 			private void ApplyPadding(Thickness padding)
 			{
-#if __IOS__
-				// Requeue the set of padding to prevent bugs with text alignment like
-				// defined in this issue: https://github.com/unoplatform/uno/issues/2836
-				Owner.Dispatcher.RunAsync(CoreDispatcherPriority.High, Set);
-
-				void Set()
-#endif
+				if (Owner.SetPadding(padding) && _log.Value.IsEnabled(LogLevel.Debug))
 				{
-					if (Owner.SetPadding(padding) && _log.Value.IsEnabled(LogLevel.Debug))
-					{
-						_log.Value.LogDebug($"ApplyPadding={padding}");
-					}
+					_log.Value.LogDebug($"ApplyPadding={padding}");
 				}
 			}