Edited Issue: IntegerUpDown 'Text' is empty when 'Value' equals to the 'DefaultValue' [21203]

Initializing IntegerUpDown control with Value == DefaultValue results in empty Text field.
This is probably due to the addition of:

```
bool shouldKeepEmpty = !forceTextUpdate && string.IsNullOrEmpty( Text ) && object.Equals( Value, DefaultValue ) && !this.DisplayDefaultValueOnEmptyText;
```

In UpDownBase class under "SyncTextAndValueProperties" method.

A workaround is to set DisplayDefaultValueOnEmptyText="True".

Sample code to demonstrate the problem:

#View -
```
<xctk:IntegerUpDown Minimum="1" Maximum="300" DefaultValue="30" Value="{Binding SampleData}"></xctk:IntegerUpDown>
```

#ViewModel - (should be initialized with 'SampleData' equals to 30)
```
DataContext = _dataContext;
_dataContext.SampleData = 30;
```

#Result -
UpDownControl with empty text field.

If the default value is different than 30, or DataContext's 'SampleData' property is initialized with value other than the DefaultValue, the Text field is shown.