Feature: a new mixing method for magnetic calculations

[WHUweiqingzhou]

Linked Issue

Fix #3225

What's changed?

1. Add Functions to Allocate/Destroy/Calculate magnetic density array
2. Change mix_rho
3. Change Kerker and inner product with new rho input
4. change default value of mixing
5. remove charge_mixing::autoset()
6. Add corresponding documentation
7. Fix charge_mixing_test
8. update some CI tests by setting mixing_gg0=0.0

Note:
This PR will introduce some warnings in CI tests even with nspin=1 since it changes the default value of mixing_gg0 from 0.0 to 1.0, you can fix them by adding mixing_gg0=0.0 in INPUT file.

Please see detail and heavy tests in documentation A new mixing method for magnetic calculations