Methods decorated with lazy do not look like data descriptors

[Ryan J Ollos]

The lazy class doesn't implement the __set__ method, so it doesn't look like a data descriptor. This was discussed in #11684.

In implementing the __set__ method, we need to decide whether methods decorated with lazy should behave like read-only properties. Another approach would be to add a lazyproperty class for lazily-evaluated attributes that should be readonly.