Make ByReference<T> public and remove the obsolete language restrictions on the use of TypedReference. Alternatively, support ref fields in ref structs.
Motivation: Performance improvement in reflection-like or serialization APIs that return interior pointers into heap objects along with additional metadata.
Details: Discussed extensively on the C# language github. Note that it can be already trivially implemented (see appendix) with ref structs that wrap a Span<T>, but that approach has the overhead of having to store the length of the span.