[WPF] Move ExTreeViewItem brush styles from template to outer style (#801)
[WPF] Move ExTreeViewItem brush styles from template to outer style (#801)

This should not change the appearance or behavior, but should make it
easier to override these styles externally.
lytico/xwt,TheBrainTech/xwt,mono/xwt,antmicro/xwt,hwthomas/xwt,hamekoz/xwt