weak search

[lf-]

Make it possible to disable the heuristic if we are not finding anything while using it. Also, consider including searching non-functions in this heuristic-disabled case.

motivation:

dev/nixpkgs - [master●] » nix-doc runtimeShell
dev/nixpkgs - [master●] » rg 'runtimeShell ='
pkgs/top-level/all-packages.nix
8043:  runtimeShell = "${runtimeShellPackage}${runtimeShellPackage.shellPath}";