Support rewinding to event in the same process, or via breakpoints

Currently, the run [event_number] command terminates the existing process, and spawns a new one. Some IDE gdb-based debuggers (e.g.: CLion) detect this and immediately detach, which causes the rr server to shut down (see also #1990). This is unfortunate if reaching the bug event takes a long time, so we would like to avoid shutting down the rr server.

A workaround for this would be either to introduce a version of the run command which rewinds inside the existing process, or, to quote @rocallahan, to do this by setting an event-based breakpoint:

I think the right solution here might be a special rr command to go to
a specific event number by issuing a special command that sets a
breakpoint at that event number and then continuing in the correct
direction. I don't think that would be very hard to do at this point,
at least if you don't mind stopping if a regular breakpoint/watchpoint
is hit along the way, and you stay in the same process.

Start at the implementation of the run [event_number] command and trace how it terminates the existing process and spawns a new one. Compare the two proposed approaches: rewinding in the same process or setting an event-based breakpoint and continuing in the correct direction. Done means reaching the requested event without shutting down the rr server or causing the debugger to detach.