ddCOSMO not variational

[lukaswittmann]

Describe the bug
ddCOSMO energy is not variational. Thus, this also applies to CPCM-X.
This also applies to tblite and its ddcpcm.

To Reproduce
Easy to reproduce using NaCl and water:

2

Na 0 0 0
Cl 0 0 1.5

via xtb nacl.xyz --cosmo water

Output during SCC:

 iter      E             dE          RMSdq      gap      omega  full diag
   1     -4.8764669 -0.487647E+01  0.386E+00    5.88       0.0  T
   2     -4.8820210 -0.555413E-02  0.234E+00    5.26       1.0  T
   3     -4.8900739 -0.805288E-02  0.281E-01    4.37       1.0  T
   4     -4.8893756  0.698224E-03  0.186E-01    4.48       1.0  T
   5     -4.8891790  0.196604E-03  0.100E-01    4.52       1.0  T
   6     -4.8895562 -0.377156E-03  0.302E-02    4.48       2.3  T
   7     -4.8895093  0.468651E-04  0.953E-03    4.48       7.4  T
   8     -4.8894764  0.329602E-04  0.825E-04    4.48      85.7  T
   9     -4.8894765 -0.155453E-06  0.390E-05    4.48    1813.1  T
  10     -4.8894765  0.287508E-07  0.974E-06    4.48    7258.5  T

with the final energy:

         :: SCC energy                -4.889476488844 Eh    ::

The final energy is not the lowest energy.