Clarify path logging line in GenericModelMaker

[alexbeattie42]

Brief summary of changes

This clarifies the path logging line in the GenericModelMaker. When I was trying to use absolute paths with the tool, I initially suspected there was something wrong with the path handling. It was challenging to debug and I eventually determined the absolute path handling was done correctly in SimTK but the logging output wasn't correct so I was getting an output like this:

Loading marker set from '/home/alexbeat/data/kg-all-trials-v1/16//home/alexbeat/AlexDev/opensim-domu/build/bin/kg_Scale_MarkerSet.xml'.

This fixes the logging output so that it outputs the exact path that will be in use after the call to SimTK::Pathname::getAbsolutePathnameUsingSpecifiedWorkingDirectory, which aids in proper inspection and debugging of path handling.

Testing I've completed

Compiled and ran locally

Looking for feedback on...

CHANGELOG.md (choose one)

• no need to update because it is a single line change to logging

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This change is 

[alexbeattie42]

@nickbianco can you take a look?

[nickbianco]

Thanks @alexbeattie42!