[Core] Explicit x vector in getPotentialEnergy

[alxbilger]

Allow to define the x vector as an input of getPotentialEnergy, instead of implicitly relying on the x vector from mparams.

Similar to #6281

[ci-depends-on https://github.com/SofaDefrost/Cosserat/pull/188]

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• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
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• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[sofabot]

[ci-depends-on] detected during build #2.

To unlock the merge button, you must

• Merge or close adapt to #6288 (getPotentialEnergy) SofaDefrost/Cosserat#188
  For this build, the following CMake flags will be set
  -DCOSSERAT_GIT_REPOSITORY='https://github.com/SofaDefrost/Cosserat'
  -DCOSSERAT_GIT_TAG='f394ded0d4f55df65f9eb808a15a5701ca458fb5'

[hugtalbot]

minor conflict @alxbilger but I prefer letting you fix it, then ✔️

[hugtalbot]

I just merged the previous one @alxbilger
therefore a few minor conflicts as expected