[Rd] Adding support for S7 to base R

[Duncan Murdoch]

One more comment:

The utils::setBreakpoint() function should be updated to be able to set 
breakpoints in S7 methods, or a substitute function should be added to 
the S7 package.

RStudio 2022.12.0+353 (not sure if that's the latest) also needs to be 
taught how to do that, since it doesn't seem to use setBreakpoint.

Duncan Murdoch