Changes

Summary

1. [Spring] Extract LinearSpring class in its own file (#4454) (details)

Commit 28b02c2df77c1ff1623b224bc0826ec38110e38c by noreply [Spring] Extract LinearSpring class in its own file (#4454)
	Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/SpringForceField.cpp (diff)
	Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/SpringForceField.h (diff)
	Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/LinearSpring.h
	Sofa/Component/SolidMechanics/Spring/CMakeLists.txt (diff)
	Sofa/Component/SolidMechanics/Spring/src/sofa/component/solidmechanics/spring/LinearSpring.cpp