cgvariant

Add all built-in solvers and several ordering methods (#1)

* Introduce LLT, LU and QR solvers

* Choice of the ordering method

* Add metis support

* Optimal plugins

* Link with Metis

* find package metis

* File encoding

* Another try

* Find metis for v21.12

* Fix CMakeLists.txt

* unused variable

* Remove find_package of metis

* Missing template keyword

* find_package SofaFramework

* Make sure the linear solver module is found

* Replace hard-coded value

* Condition on finding the metis include file

* Fix missing guard

* Remove warning directive

master

release-master

Fix ci