Factor out option renaming

Option aliases/deprecations can now be declared in any NixOS module,
not just in nixos/modules/rename.nix. This is more modular (since it
allows for example grub-related aliases to be declared in the grub
module), and allows aliases outside of NixOS (e.g. in NixOps modules).

The syntax is a bit funky. Ideally we'd have something like:

  options = {
    foo.bar.newOption = mkOption { ... };
    foo.bar.oldOption = mkAliasOption [ "foo" "bar" "newOption" ];
  };

but that's not possible because options cannot define values in
*other* options - you need to have a "config" for that. So instead we
have functions that return a *module*: mkRemovedOptionModule,
mkRenamedOptionModule and mkAliasOptionModule. These can be used via
"imports", e.g.

  imports = [
    (mkAliasOptionModule [ "foo" "bar" "oldOption" ] [ "foo" "bar" "newOption" ]);
  ];

As an added bonus, deprecation warnings now show the file name of the
offending module.

Fixes #10385.

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