GridVariant/Grid should implement ThemeVariant/HasThemeVariant

[Frettman]

GridVariant doesn't implement ThemeVariant yet and Grid is missing HasThemeVariant. Unless there's a reason they don't? Just seems like a small oversight.

[vursen]

Thanks, this is indeed most likely an oversight. There seem to be other components missing it as well, such as GridPro. To fix this in a minor version, without breaking binary compatibility, we could probably add this interface to those components and temporarily update their own methods like addThemeVariants to call super.