reflect: add a range like interface for Value #11104
Description
The current reflect.Value interface for traversing maps requires allocating
all the keys at once (reflect.Value.MapKeys), which is not efficient for
huge maps.
Additionally, as floating point NaNs are never equal to each other, the
current interface makes it impossible to get the value for NaN keys.
We can introduce this
func (v Value) MapKeyValues() [][2]Value
to solve the NaN problem, but I'm more interested in the first problem.
Actually, if we decide to introduce a range like operation on reflect.Value,
I think we should make it work for other range-able types (channels,
arrays, strings and slices) too.