IOC Record simulation: allow selection of subset of multiple devices

One for discussion. If an IOC talks to multiple devices, and one of these devices fails to communicate, it might be useful to put just that individual device into record simulation and keep the rest working normally. This would allow e.g. an appropriate value to be recorded in a block if for example the device was still working but needed manual control.

This could be accomplished by having a per device "in simulation" pv, then the usual global simulation pv (set from the configuration) pushes to all these. By caputs a user could then temporarily enable/disable simulation mode on a per device basis for that ioc after startup, but the global configuration default will be reasserted on next startup.