[Orc] Add AutoRegisterCode option for DebugObjectManagerPlugin

Configure the plugin to automatically call the debugger rendezvous breakpoint `__jit_debug_register_code()` for every translation unit (enabled) or never at all (disabled). Default API and behavior remain unchanged.

If AutoRegisterCode is turned off, it's the client's own responsibility to call the rendezvous breakpoint function at an appropriate time.
Depending on the complexity of the debugger's rendezvous breakpoint implementation, this can provide significant performance improvements in cases where many debug objects are added in sequence.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D147310