Please make some classes in simulator package public for simulator customization.

[zhutmost]

Type of issue: Feature Request

Is your feature request related to a problem? Please describe.
I want to customize the simulation process with svsim. But some important classes in [chisel3/simulator/package] are private, such as:

• class SimulatedModule has a private constructor. It should be public, or I cannot create one during simulation.
• object AnySimulatedModule is private. please make it public. Or users cannot use its methods withValue and current.
• class AnySimulatedModule is sealed (cannot be extended) and has many private/protect methods.

I am writing some new things like PeekPokeAPI and EphemeralSimulator. And the above APIs are private so that I cannot access them (unless I fork a whole chisel).

Describe the solution you'd like
make the above simulator's APIs public.

Describe alternatives you've considered
N/A.

Additional context
N/A.

What is the use case for implementing this feature?