Mention "kOfxMeshEffectPropContext" etc. in documentation

[tkarabela]

• https://github.com/eliemichel/OpenMfx/blob/e0807499328e78f4c8cad56689c554cb4776e5e9/doc/Reference/ofxMeshEffectActions.rst
  • this page should mention kOfxMeshEffectActionDescribeInContext in the "Actions specific to Mesh Effects" section
  • currently it only mentions in docs for kOfxActionDescribe that "kOfxImageEffectActionDescribeInContext will be called once for each context that the host and plug-in mutually support" which is not correct
• https://github.com/eliemichel/OpenMfx/blame/e0807499328e78f4c8cad56689c554cb4776e5e9/doc/Reference/ofxMeshEffectAPI.rst#L30-L41
  • kOfxMeshEffectPropContext, kOfxMeshEffectContextGenerator etc. have Doxygen documentation but are commented out in the Sphinx docs so they don't show up