[wpiutil] RFC: Add mechanism to register global reset functions

[virtuald]

Intent would be to get rid of most of the wpi::impl/frc::impl functions I've added for RobotPy and provide a way for teams to reset wpilib between unit tests as well. Would also provide a mechanism for vendor state to be reset if they participated.

Let's start by talking about this, and if we think this isn't terrible, then I can actually replace the existing reset functions I'm aware of with this and add those to the PR.

CC @Starlight220

[virtuald]

/format

[Starlight220]

The concept looks good!
One thing I'm not sure about is how Java would work with this, regarding @PeterJohnson 's comment here. Wouldn't this create dangling references as well?

[virtuald]

Java has its own versions of all the singletons I'm thinking about, so it would need its own implementation of this sort of thing. I am not going to implement that.

[virtuald]

Couple things I ran into when baking this:

• NetworkTables is actually a bit more involved than I had thought through at first. Likely you'd want to reset the default instance and destroy every other instance -- which I don't even do for my tests.
• There are some robotpy-specific things that I need to do when some of these are reset, which I thought I'd be able to do by inserting my own priorities, but that isn't actually the case.
• It's not clear to me if the ordering I have defined here is really the Right Order. I currently follow this order in RobotPy, but I have changed it when crashes occurred.

[virtuald]

/format

[virtuald]

I don't understand why tidy/format are failing here.