CMake >= 3.19 required. Improve Find[SCA]LAPACK with MKL

For those using MKL match library to provide LAPACK and SCALAPACK, we now use Intel's MKLConfig.cmake as recommended. For those using MKL, MKL 2021.3 or newer is required.

CMake >= 3.19 required to avoid vendoring so much much code and to remove workaround logic.