MOLGW package: fix dependence to threaded MKL (#39028)

* molgw package.py

* molgw package.py almost ready

* bug fix in molgw package.py

* MOLGW v3.2

* black pass

* duplicated line eliminated

* remove FIXME in the header

* add me as a maintainer

* fix previous commit

* sort the imports in the order spack wants

* chop the too-long lines

* many fixes

- variants before dependences
- eliminate useless build and install stages
- no openmp with intel-mkl was broken

* after blackization

* cleaning

* Update var/spack/repos/builtin/packages/molgw/package.py

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

* Update var/spack/repos/builtin/packages/molgw/package.py

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

* Update var/spack/repos/builtin/packages/molgw/package.py

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

* Update var/spack/repos/builtin/packages/molgw/package.py

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

* Update var/spack/repos/builtin/packages/molgw/package.py

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

* use threaded mkl when openmp is triggered

---------

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>