This pull request fixes #11306 via a rework of the constraint symbol framework:

• A SoMultipleCopy node is used to create multiple copies of the symbol node and save resources (currently, there is one node for each symbol).

• The symbol geometry is read from an Open Inventor .iv file (the expected file structure is detailed in the loadSymbol function documentation) and is made up of the symbol used at each point on the reference shape plus an optional symbol that does not is affected by multiple copies (for example, useful for those constraints that need to use a global symmetry axis).

• Some attributes are added for fine control over the symbol:

  • An extra symbol node to add a global symbol not affected for transformations at each point on the reference shape.
  • A boolean to set whether to apply local rotations based on the reference geometry normal vectors or set the multiple
    copied to remain oriented in the same direction and only translate rigidly (for example, displacement constraint symbol).

• Control nodes and attributes are also exposed to ViewProviderFemConstraint Python Features.

• A virtual transformSymbol function to apply local transformations to the symbol at each point on the reference.

  So, to add symbols to proxy Python objects:

  class VPConstraintProxy:
       ...
       def attach(self, vobj):
           # vobj.loadSymbol(path_to_iv_file)
           # vobj.RotateSymbol = True/False
       ...
       def updateData(self, vobj, prop):
           # apply changes to the symbol using vobj.SymbolNode, vobj.ExtraSymbolNode
  

There are still some objects to migrate: Constraint transform and the hidden constraints bearing, gear, pulley and fluidBoundary.
After these objects are migrated, the static ViewProviderFemConstraint methods used to create symbols are obsolete and can be removed.