particlesPath and meshesPath should be required different #291
Description
Having particlesPath and meshesPath equal would probably cause issues with parsers. It would make it hard to distinguish mesh records with particle records.
Consequently, I suggest that the standard forbids having these paths equal. Note that the equality should not be only in terms of the strings that these variables contain: the path resolution should lead to distinct locations. For instance, soft links or .. placeholders could lead to path equality.
[This is a followup on openPMD/openPMD-viewer/issues/433]