Mismatch about default collision detector between SDFormat specification and Gazebo Sim documentaion

[xela-95]

Hi,

I noted that the SDF documentation about the default collision detector is different from the Gazebo sim one:

• SDF says fcl: http://sdformat.org/spec?ver=1.11&elem=physics#dart_collision_detector
• Gazebo sim says ode:

  gz-sim/tutorials/physics.md

  Line 100 in 6cfcd07

  * Options supported by DART: `ode` (default), `bullet`, `fcl`, `dart`.

  (also used in unit tests https://github.com/gazebosim/gz-physics/blob/7d30e47fb61fe4db9cba460717a3910df9deabee/dartsim/src/WorldFeatures_TEST.cc#L87)

[traversaro]

My guess is that "fcl" is the Gazebo Classic default, while "ode" is the modern gz-sim default, but I did not double checked.

xref to a kind of generic issue related to this: gazebosim/sdformat#508

[azeey]

From Ian: Maybe we should at least print a warning that the default is being overridden in gz-sim

[azeey]

Another thought is that we have a dedicated page in the gz-sim documentation that indicates which SDF tags gz-sim actually supports.