Review of Reference change regarding receivers and object safety

[traviscross]

There are two outstanding changes to the Reference regarding receiver types and object safety:

• Update object safety to match impl around self as receiver reference#1248
• Document how self: Self receiver types *actually* interact with object safety reference#1455

These are related to an outstanding issue filed against the Reference here:

• Rule around non-dispatchable functions doesn't match the compiler behavior reference#1247

The rustdocs team would appreciate a review by @rust-lang/types on whether one or both or these PRs are correct and whether the types team (or interested members thereof) would like to see any changes before these are merged.

@rustbot labels +T-types +I-types-nominated

[ehuss]

One other minor thing that would be nice to look at while you are thinking about object-safe rules is rust-lang/reference#756. Someone provided a suggestion for the addition there, and it would be nice for someone to confirm it.