Add resource for TextBox border tickness when pointer is over

[mgnslndh]

Would you accept a PR that adds a resource TextControlBorderThicknessPointerOver that is applied to the BorderThickness when the trigger IsMouseOver is true? The default value would be the same as TextControlBorderThemeThickness but it would allow a theme to override the thickness without restyling the control template.

[ShankarBUS]

If the same behaviour is applicable in WinUI, the author would accept the PR.

[mgnslndh]

I guess it could be applicable to WinUI but it is not present in the current WinUI style for the TextBox.

https://github.com/microsoft/microsoft-ui-xaml/blob/31ca62bb0e37b088f09b7953cf5958d2af3fa718/dev/CommonStyles/TextBox_themeresources.xaml#L212-L229

What do you mean by applicable? Does it need to be supported by WinUI first in order for ModernWpf to support it?

[Kinnara]

Does it need to be supported by WinUI first in order for ModernWpf to support it?

This is usually the case, since this library tries to match WinUI closely. There are exceptions due to platform differences, but for a XAML resource like this one, WinUI will need to add it first.