Request: Make an optional_ref<T>

[drewr95]

Currently, I use pointers to discern optional references but I think it would be better to be more explicit with an optional_ref type since optional can't hold them (and probably rightfully so).

[rolandreichweinbmw]

How about: etl::optional<etl::reference_wrapper<T>> ?

[jwellbelove]

An optional_ref<T> would be fairly simple to implement, as internally it would just wrap a T*.
A non-valid optional_ref<T> would just contain a nullptr.