Classes should be completed

Describe the bug

When you start writing the classes property on an element, Intellisense does not propose the Classes property.

To Reproduce

Do not work

        [Fact]
        public void Classes_Attribute_Should_Be_Completed()
        {
            AssertSingleCompletion("<Button ", "Cla", "Classes=\"\"");
        }

Work

        [Fact]
        public void Classes_Should_Be_Completed()
        {
            AssertSingleCompletion("<Button><Button.", "Cla", "Classes");
        }

AvaloniaVS plugin version

11.0.0

Avalonia version

11.0.0 and upper

Visual Studio version

No response

Relevant log output

Last work 11.0-preview4

Additional context

Intellisense don't working after PR https://github.com/AvaloniaUI/Avalonia/pull/11013 because it makes the Classes property read-only.

AvaloniaUI / AvaloniaVS

Classes should be completed #376