Converting use of property variables to getter method calls in DeGrooteFregly2016Muscle

[AllisonJohn]

Fixes issue #3483

Brief summary of changes

• Made get methods for the properties so that they can update more often
• Replaced all usages of the instance variables with get method calls, got rid of variables
• Except for m_isTendonDynamicsExplicit because it would cause errors

Testing I've completed

• running testDeGrooteFregly2016Muscle
• [perf-win]
• using the HangingMuscleModel example, added the properties as parameters and checked that they changed after the solve

Looking for feedback on...

Previously extendFinalizeFromProperties had several checks for the properties before changing the variables. So is it a problem if we are now changing the variables without doing these checks?

CHANGELOG.md (choose one)

• updated.

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