move scidoc to docstrings of individual stencils

[halungge]

Move the #scidoc strings from SolveNonHydro and VelocityAdvection to the doc string of the individual stencil field operators.

• Adapted some of the outputs and input namings where they changed from the stencil call to the stencil implementation
• Split some of the #scidocs were they collected previousely fused stencils that most likely will not longer be used.

[github-actions]

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[halungge]

cscs-ci run default