Use consistent wording for binding warnings.

"Could not convert" instead of "Cannot convert".

src/Avalonia.Base/Data/Core/BindingExpression.cs

@@ -186,7 +186,7 @@ internal class BindingExpression : IObservable<object?>,
                 var valueString = value?.ToString() ?? "(null)";
                 var valueTypeName = value?.GetType().FullName ?? "null";
                 var ex = new InvalidCastException(
-                    $"Cannot convert '{valueString}' ({valueTypeName}) to {type}.");
+                    $"Could not convert '{valueString}' ({valueTypeName}) to {type}.");
                 _observer?.OnNext(new BindingNotification(ex, BindingErrorType.DataValidationError));
                 return false;
             }
@@ -555,7 +555,7 @@ internal class BindingExpression : IObservable<object?>,
             var valueString = value?.ToString() ?? "(null)";
             var valueTypeName = value?.GetType().FullName ?? "null";
             var ex = new InvalidCastException(
-                $"Cannot convert '{valueString}' ({valueTypeName}) to {targetType} using '{converter}'.", e);
+                $"Could not convert '{valueString}' ({valueTypeName}) to {targetType} using '{converter}'.", e);
             return new BindingNotification(ex, BindingErrorType.Error);
         }
     }
@@ -572,7 +572,7 @@ internal class BindingExpression : IObservable<object?>,
             Log(target, $"Could not convert {fallbackName} '{fallback}' to '{TargetType}'.", LogEventLevel.Error);
 
         return AvaloniaProperty.UnsetValue;
-   }
+    }
 
     private object? ConvertFrom(TargetTypeConverter? converter, object value)
     {
@@ -586,7 +586,7 @@ internal class BindingExpression : IObservable<object?>,
 
         var valueString = value?.ToString() ?? "(null)";
         var valueTypeName = value?.GetType().FullName ?? "null";
-        var message = $"Cannot convert '{valueString}' ({valueTypeName}) to '{targetType}'.";
+        var message = $"Could not convert '{valueString}' ({valueTypeName}) to '{targetType}'.";
 
         if (ShouldLogError(out var target))
             Log(target, message, LogEventLevel.Warning);

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.cs

@@ -112,7 +112,7 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
             Assert.Equal(
                 new BindingNotification(
-                    new InvalidCastException("Cannot convert 'foo' (System.String) to 'System.Int32'."),
+                    new InvalidCastException("Could not convert 'foo' (System.String) to 'System.Int32'."),
                     BindingErrorType.Error,
                     42),
                 result);
@@ -134,7 +134,7 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
             Assert.Equal(
                 new BindingNotification(
-                    new InvalidCastException("Cannot convert 'foo' (System.String) to 'System.Int32'."),
+                    new InvalidCastException("Could not convert 'foo' (System.String) to 'System.Int32'."),
                     BindingErrorType.Error,
                     42),
                 result);
@@ -251,7 +251,7 @@ namespace Avalonia.Base.UnitTests.Data.Core
                     new BindingNotification($"{1.2}"),
                     new BindingNotification($"{3.4}"),
                     new BindingNotification(
-                        new InvalidCastException("Cannot convert 'bar' (System.String) to System.Double."),
+                        new InvalidCastException("Could not convert 'bar' (System.String) to System.Double."),
                         BindingErrorType.DataValidationError)
                 },
                 result);

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests_DataValidation.cs

@@ -102,7 +102,7 @@ namespace Avalonia.Base.UnitTests.Data.Core
 
                 // Exception is thrown by trying to set value to "foo".
                 new BindingNotification(
-                    new InvalidCastException("Cannot convert 'foo' (System.String) to System.Int32."),
+                    new InvalidCastException("Could not convert 'foo' (System.String) to System.Int32."),
                     BindingErrorType.DataValidationError),
 
                 // Value is set then validation is updated.

tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs

@@ -242,7 +242,7 @@ namespace Avalonia.Markup.UnitTests.Data
                 using (AssertLog(
                     target,
                     binding.Path,
-                    "Cannot convert '0.0' (System.Version) to 'Avalonia.Thickness'.",
+                    "Could not convert '0.0' (System.Version) to 'Avalonia.Thickness'.",
                     property: Control.MarginProperty))
                 {
                     target.Bind(Control.MarginProperty, binding);