Add R2SCAN functional from libxc

afonarirequested to merge
(removed):r2scan-develop into develop

Added r2scan similar to scan and scan0 (hopefully it is correct). Tested by comparing energies between scan and r2scan results.

Fixed a bug in xclib_get_dft_short(), SCAN0 wasn't returned as short name since meta number was wrong (263 vs. 264).

IDs of the functionals in libxc are here: https://www.tddft.org/programs/libxc/functionals/

Pinging @fabrizio22.

Merge request reports