[tracking] Command-based improvements

[Starlight220]

This refers to specifically commands themselves, not the button bindings stuff (that's in #4218). All this is subject to change and happily up for discussion.

• [x] #4245

• [x] #4179

• [x] #3536

• [ ] #4386 onInterrupt decorator - would subsume #4021

• [ ] #4303

• [ ] #4236

Further directions:

• way to break out of a sequential group from inside it
• Command builders
• (possibly?) user-defined infix decorators
• Anything else?

[Daltz333]

Another thing. Any PR that seeks to close this issue should also make corresponding PR(s) to frc-docs.