Changed Span default binding to OneWay (#4850)

Xamarin.Forms.Core/Span.cs

@@ -15,7 +15,7 @@ namespace Xamarin.Forms
 		}
 
 		public static readonly BindableProperty StyleProperty = BindableProperty.Create(nameof(Style), typeof(Style), typeof(Span), default(Style),
-			propertyChanged: (bindable, oldvalue, newvalue) => ((Span)bindable)._mergedStyle.Style = (Style)newvalue, defaultBindingMode: BindingMode.OneTime);
+			propertyChanged: (bindable, oldvalue, newvalue) => ((Span)bindable)._mergedStyle.Style = (Style)newvalue, defaultBindingMode: BindingMode.OneWay);
 
 		public static readonly BindableProperty TextDecorationsProperty = DecorableTextElement.TextDecorationsProperty;
 
@@ -26,7 +26,7 @@ namespace Xamarin.Forms
 		}
 
 		public static readonly BindableProperty BackgroundColorProperty
-			= BindableProperty.Create(nameof(BackgroundColor), typeof(Color), typeof(Span), default(Color), defaultBindingMode: BindingMode.OneTime);
+			= BindableProperty.Create(nameof(BackgroundColor), typeof(Color), typeof(Span), default(Color), defaultBindingMode: BindingMode.OneWay);
 
 		public Color BackgroundColor
 		{
@@ -55,7 +55,7 @@ namespace Xamarin.Forms
 #pragma warning restore 618
 
 		public static readonly BindableProperty TextProperty
-			= BindableProperty.Create(nameof(Text), typeof(string), typeof(Span), "", defaultBindingMode: BindingMode.OneTime);
+			= BindableProperty.Create(nameof(Text), typeof(string), typeof(Span), "", defaultBindingMode: BindingMode.OneWay);
 
 		public string Text
 		{