Feature: output dkin for metaGGA calculations

[WHUweiqingzhou]

Fix #3562 and #3146.

Why

In addition to charge density, kinetic density also needs to be considered in metaGGA calculations. Sometimes, the drho is very close to zero, while the EDIFF is rather large, which confuse the user. The finite EDIFF comes from the kinetic density instead of charge density. To avoid similar confusion, it is necessary to output the kinetic density difference at each iteration.

List of Changes

1. add a new parameter DKIN into printhead()
2. add a new parameter dkin into printetot(), print_etot(), printiter()
3. add a get_dkin(), similar with get_drho()

Results

I take abacus-develop/tests/integrate/216_NO_scan_Si2 as an example:
Old:

DONE(0.358404   SEC) : INIT SCF
 ITER   ETOT(eV)       EDIFF(eV)      DRHO       TIME(s)    
 GE1    -2.045033e+02  0.000000e+00   2.945e-01  4.466e-01  
 GE2    -2.034444e+02  1.058872e+00   1.150e-01  3.721e-01  
 GE3    -2.034414e+02  2.967687e-03   8.388e-03  3.721e-01  
 GE4    -2.034731e+02  -3.164552e-02  2.183e-03  3.735e-01  
 GE5    -2.034720e+02  1.056283e-03   1.013e-04  3.734e-01  
 GE6    -2.034726e+02  -6.129378e-04  1.181e-05  3.735e-01  
 GE7    -2.034727e+02  -1.090943e-05  3.115e-06  3.733e-01  
 GE8    -2.034727e+02  -3.161632e-07  2.331e-07  3.734e-01  
 GE9    -2.034727e+02  2.201660e-09   7.833e-08  3.741e-01  
 GE10   -2.034727e+02  1.750779e-08   6.904e-09  3.734e-01  
 GE11   -2.034727e+02  -8.487448e-09  7.649e-10  3.723e-01  

New:

DONE(0.273942   SEC) : INIT SCF
 ITER   ETOT(eV)       EDIFF(eV)      DRHO       DKIN       TIME(s)    
 GE1    -2.045033e+02  0.000000e+00   2.945e-01  4.232e-01  4.448e-01  
 GE2    -2.034444e+02  1.058872e+00   1.150e-01  9.808e-03  3.772e-01  
 GE3    -2.034414e+02  2.967687e-03   8.388e-03  8.195e-03  3.763e-01  
 GE4    -2.034731e+02  -3.164552e-02  2.183e-03  4.036e-04  3.761e-01  
 GE5    -2.034720e+02  1.056283e-03   1.013e-04  1.573e-04  3.765e-01  
 GE6    -2.034726e+02  -6.129378e-04  1.181e-05  1.657e-05  3.747e-01  
 GE7    -2.034727e+02  -1.090943e-05  3.115e-06  4.633e-07  3.751e-01  
 GE8    -2.034727e+02  -3.161632e-07  2.331e-07  2.111e-07  3.745e-01  
 GE9    -2.034727e+02  2.201660e-09   7.833e-08  5.770e-08  3.763e-01  
 GE10   -2.034727e+02  1.750779e-08   6.904e-09  1.108e-08  3.773e-01  
 GE11   -2.034727e+02  -8.487448e-09  7.649e-10  1.270e-09  3.759e-01

[dyzheng]

DKIN info is useful to meta-gga functional users.