next-gtk-webkit: init at 1.5.0

[bqv]

Motivation for this change

Break off next-gtk-webkit into it's own package, so builds happen and it can be overriden nicely.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[worldofpeace]

Hmm, not sure how I feel about this. I believe I refactored this package and next-gtk-webkit was exposed, but I made it private seemingly without qualms and good justification. Can't recall exactly though.

[bqv]

The alternative I see is to move all inputs from next-gtk-webkit to next so it can be nicely overridden, but I can't see any obvious issues with this

[bqv]

(Thinking something along the lines of 829f41459f2a1d4ef81c0627f761959c5da4bcab)

[bqv]

Hmm, seems next-gtk-webkit is about to die (see atlas-engineer/nyxt#422 (comment)), this can go away :)