nixpkgs Google Sans Code attr names and Nerd Font families

In nixpkgs the plain font is pkgs.googlesans-code (not google-sans-code), and the Nerd Font build is pkgs.nerd-fonts.googlesanscode. The patched families are 'GoogleSansCode Nerd Font', 'GoogleSansCode Nerd Font Mono' and 'GoogleSansCode Nerd Font Propo' (no space in GoogleSansCode), which is what stylix fonts.monospace.name / sansSerif.name need. Metrics: x-height 0.52 em, cap height 0.716, advance 0.6, versus Terminess Nerd Font at 0.458 x-height, so drop point sizes by roughly 14% when switching from Terminess. Verify family names with fc-scan --format '%{family}\n' on the built store path before writing them into config.