Functions to enable velocity and acceleration checks on Link

[chapulina]

🎉 New feature

Summary

This is broken off #926 for easier review.

The Link class provides convenient functions to retrieve velocities and accelerations without needing to touch the ECM directly. But in order to use those functions, users need to create the necessary components. This defeats the purpose of having an API that hides away the ECM's complexity.

This PR adds the Enable(Velocity|Acceleration)Checks functions, which provide a way for users of the Link API to create those components without necessarily knowing that they're doing so.

Test it

I used the new functions in some existing plugins to demonstrate how it comes in handy for plugin developers, see below. The tests and documentation should also be helpful to understand the intended usage.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

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[codecov]

Codecov Report

Merging #935 (17f4473) into ign-gazebo3 (847b1ae) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 17f4473 differs from pull request most recent head 1c444a6. Consider uploading reports for the commit 1c444a6 to get more accurate results

@@               Coverage Diff               @@
##           ign-gazebo3     #935      +/-   ##
===============================================
- Coverage        77.83%   77.79%   -0.05%     
===============================================
  Files              219      220       +1     
  Lines            12593    12562      -31     
===============================================
- Hits              9802     9772      -30     
+ Misses            2791     2790       -1     

Impacted Files	Coverage Δ
include/ignition/gazebo/Link.hh	100.00% <ø> (ø)
include/ignition/gazebo/Util.hh	100.00% <100.00%> (ø)
src/Link.cc	93.54% <100.00%> (+1.51%)	⬆️
...ems/kinetic_energy_monitor/KineticEnergyMonitor.cc	82.69% <100.00%> (-2.16%)	⬇️
src/systems/lift_drag/LiftDrag.cc	69.93% <100.00%> (-1.68%)	⬇️
src/systems/wind_effects/WindEffects.cc	79.32% <100.00%> (-0.23%)	⬇️
src/Server.cc	82.80% <0.00%> (-1.54%)	⬇️
src/Util.cc	92.96% <0.00%> (-0.08%)	⬇️
src/SimulationRunner.cc	94.42% <0.00%> (-0.07%)	⬇️
src/SimulationRunner.hh	100.00% <0.00%> (ø)
... and 3 more

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[arjo129]

These new APIs are awesome! They'll make it so much easier for systems authors (and result in lot cleaner systems). One small suggestion is lets make the helper function void enableComponent(EntityComponentManager &_ecm, Entity _entity, bool _enable) in link.cc public. There are many places where this pattern is used and it'd be incredibly helpful to reduce the complexity of systems code.

[mjcarroll]

I agree with @arjo129 that moving this enableComponent function into the public API would make a lot of sense. It's a pattern that we do a good bit throughout the codebase.

[arjo129]

LGTM. I've got a small suggestion to make that might improve quality of life but feel free to reject it if you think its inappropriate.