Add support for solving nonlinear equations via Newton-Raphson method

[nikoscham]

This issue has been added to the FEAScript roadmap for the upcoming 0.2.0 release (https://github.com/orgs/FEAScript/discussions/17).

[nikoscham]

The Newton-Raphson method has been implemented (see the code https://github.com/FEAScript/FEAScript-core/blob/main/src/methods/newtonRaphsonScript.js and the example https://feascript.com/tutorials/solidification-front-2d.html). Further optimization is still required.