Native simulation for other pipelines

[axyklee]

Is your feature request related to a problem? Please describe.
Currently, PhotonVision only includes native (integrated with WPILIB) simulation fo AprilTags. This is expected, as AprilTag locations are expected and can be rendered in-time. However, it would also be helpful to be able to simulate other pipelines without rendering them.

Describe the solution you'd like
Create Sim classes for other pipelines that would be used only in simulation. The source could be a native camera stream (although that would have to deal with ffmpeg), or an FRC-specific CameraStream on the Network Tables (I assume this is the easier implementation).

Describe alternatives you've considered

1. PhotonVision could use a CameraServer as a source regardless of whether the robot is real or simulated, instead of requiring users to use onboard webcams. I understand that the architecture of PhotonVision makes this unrealistic.
2. Currently, teams achieve this function by running an instance of PhotonVision on their computer and publishing their AdvantageScope camera renders as a camera stream using OBS. However, this process is quite cumbersome and difficult to replicate, and would be greatly enhanced if integrated natively.

[axyklee]

This feature request from AdvantageScope can be very well integrated with PhotonVision: Mechanical-Advantage/AdvantageScope#169 (comment)