Add @since annotations for base instances
Up until now we haven't been adding
@since annotations for instances that we add to
base (see D2051 for the discussion that spurred this ticket). We should try to get better coverage here.
Unfortunately, we currently have no way to place Haddock comments on derived instances, which limits our ability consistently add these annotations. We'll need to work out some mechanism for this (see #11768 (closed)).