Add mech support for PinMAME

[freezy]

PinMAME offers mech simulation, i.e. it can drive a motor for you and toggle switches if necessary. Most of the time I've spent on this PR went actually into figuring out how it works exactly and documenting it.

The general idea is to make it easy for creators to use PinMAME's mech sim if desired, but be able to easily swap it out by a custom component if necessary. We'll provide such components at some point, right now the only one is called StepRotatorMechComponent and just does linear movement for a defined length.

If you actually want to use this (our use case is the T2 cannon), you would use three components:

1. The PinMAME mech component that tells PinMAME to simulate the mech and outputs speed and position
2. A "cannon rotator" component that takes in that speed and position and converts it into an angle
3. And a "rotator" component that takes in the angle and applies it to the playfield geometry (and balls, if necessary).

Each component could be swapped by another one, giving you "bricks" to adapt to your game logic. It's currently pretty basic, but it's a good foundation for more complex setups. In the future we could support node graphs where you could basically do whatever you need to compute, graphically.

By the way I did plot how the cannon of T2 moves. Looks like a sine function, which we could reproduce quite easily, but that's for another PR.

Finally, here the T2 gun, simulated by PinMAME, in action:

https://user-images.githubusercontent.com/70426/140429006-9aaa1c92-5d71-4455-ae51-14818eb08f86.mp4

This PR also requires VisualPinball/VisualPinball.Engine.PinMAME#15, where the actual component is implemented.

[codecov[bot]]

Codecov Report

Merging #339 (fd587fa) into master (f2e1a8c) will not change coverage. The diff coverage is n/a.

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