[Feature Request] Allow character spacing to be configurable for TextBlock and TextBox controls

AFAIK, there's currently no way to change the space between characters in a TextBlock/TextBox control. Similar to how we can change the character spacing for a [TextBlock in WinUI](https://learn.microsoft.com/en-us/uwp/api/windows.ui.xaml.controls.textblock.characterspacing?view=winrt-26100), if we could do the same for WPF's TextBlock and TextBox controls, that would be pretty useful.