[WIP] Use topology-based moment arm detection in PolynomialPathFitter

[nickbianco]

Fixes issue #4348

Brief summary of changes

Leverages changes added via #4301 to find the set of coordinates in each path for which to compute moment arms. Previously, moment arms for every coordinate in the model were computed for each path which was inefficient and sometimes produced erroneous moment arms due to MomentArmSolver's force-based calculation approach. Now, we automatically detect which coordinates should belong to a path based on the model topology by finding the joints that lie between the path's origin and insertion. Moment arms are computed only for coordinates detected using this approach.

The property moment_arm_threshold has been removed, and the methods get/setMomentArmThreshold() have been deprecated. In addition, the approach for leverage thread parallelization has been modified: now each thread performs the calculations for a single path at a time, iterating over all paths until completed. This is achieved using std::atomic to store a (thread-safe) index of the current path, and the worker function in each thread operates on a while-loop until the set of paths is exhausted.

Testing I've completed

Existing CI tests, e.g., testPolynomialPathFitter.cpp. Also tested scripting example examplePolynomialPathFitter.py locally.

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