fix TagInput bug when TagsProperty changed.

[dameng324]

When TagInput's Tags changed, you want remove all the tags except the textBox from Items collection, right? But the code does not do that.

old code:

 for (int i = 0; i < Items.Count - 1; i++)
 {
     Items.RemoveAt(Items.Count - 1);
 }

Items.Count will change after every RemoveAt so If the Items.Count is 6, It only remove 3 times, then i will be 3,Items.Count will be 3, the loop will end.

So, I fix this problem.
new code:

// remove all tags except the textbox
int count = Items.Count;
for (int i = 0; i < count - 1; i++)
{
    Items.RemoveAt(0);
}

I create a repro branch(https://github.com/dameng324/Ursa.Avalonia/tree/taginput-fix-tags-changed-repo) to repro this problem. Feel free to check it.

[rabbitism]

I would suggest to count down i from Count-1( not verified) because RemoveAt(0) has very bad performance.

[dameng324]

There is always a textBox at the end of Items. RemoveAt(Items.Count-2) always move that element.

If you concern abount the performance, clear and add the textBox will be nicer ?

[rabbitism]

Once upon a time I tried but if I remembered correctly it triggered some visual parent re-attach issue, But you can try, if it works well I accept.

[dameng324]

The clear and add method works well, but I've found an even better approach. By default, Items is an AvaloniaList, which includes the RemoveRange method. This method is advantageous because it triggers the CollectionChanged event only once.

However, since the Items property is public and users may modify it, we'll need to implement a fallback mechanism. If Items is not an AvaloniaList, it will revert to the clear and add logic.

Both has been tested on my local machine.