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.

nixos/modules/system/boot/loader/grub/grub.nix

@@ -488,4 +488,15 @@ in
 
   ];
 
+
+  imports =
+    [ (mkRemovedOptionModule [ "boot" "loader" "grub" "bootDevice" ])
+      (mkRenamedOptionModule [ "boot" "copyKernels" ] [ "boot" "loader" "grub" "copyKernels" ])
+      (mkRenamedOptionModule [ "boot" "extraGrubEntries" ] [ "boot" "loader" "grub" "extraEntries" ])
+      (mkRenamedOptionModule [ "boot" "extraGrubEntriesBeforeNixos" ] [ "boot" "loader" "grub" "extraEntriesBeforeNixOS" ])
+      (mkRenamedOptionModule [ "boot" "grubDevice" ] [ "boot" "loader" "grub" "device" ])
+      (mkRenamedOptionModule [ "boot" "bootMount" ] [ "boot" "loader" "grub" "bootDevice" ])
+      (mkRenamedOptionModule [ "boot" "grubSplashImage" ] [ "boot" "loader" "grub" "splashImage" ])
+    ];
+
 }

nixos/modules/system/boot/systemd.nix

@@ -772,4 +772,11 @@ in
 
   };
 
+  # FIXME: Remove these eventually.
+  imports =
+    [ (mkRenamedOptionModule [ "boot" "systemd" "sockets" ] [ "systemd" "sockets" ])
+      (mkRenamedOptionModule [ "boot" "systemd" "targets" ] [ "systemd" "targets" ])
+      (mkRenamedOptionModule [ "boot" "systemd" "services" ] [ "systemd" "services" ])
+    ];
+
 }