[SelectField] Add a selectedMenuItemStyle property

[rdagger]

I’m trying to change the color of the selected menuItem in a SelectField. It looks like you can only change the selected color when you create a Menu component. Then you can use the selectedMenuItemStyle prop. However, the SelectField and DropDown components create the Menu inside the PopOver and the menuItem.selectedTextColor is hard coded to rawTheme.palette.accent1Color. It would be very helpful if selectedMenuItemStyle could be exposed to the SelectField component.

[alitaheri]

Hmmm this is a very good feature to have. a PR is welcome if you have the time ^_^

[oliviertassinari]

That property was exposed in #5389.