Motivation for this change

LXQt binaries look for their themes and translations based on the name of the binary, which is changed by the wrapper script. This patches liblxqt to recover the original name from the wrapped binary name. This is intended to fix #70780.

I don't know if this is the best or most general solution to the problem. The root cause is that QCoreApplication::applicationFilePath() reads /proc/self/exe to determine the binary name, which points to the renamed wrapped binary, instead of using argv[0], which points to the originally named wrapper script.

I'm not familiar with Qt, so I'm not sure what applications generally expect to use the path for. If it's mostly for locating resources relative to the binary, then I wonder if it would be better to patch Qt to read argv[0]. Consider that because of wrapQtAppsHook, /proc/self/exe will never be the original name of the binary.

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.