lib: introduce imap0, imap1 (#25543)

* lib: introduce imap0, imap1

For historical reasons, imap starts counting at 1 and it's not
consistent with the rest of the lib.

So for now we split imap into imap0 that starts counting at zero and
imap1 that starts counting at 1. And imap is marked as deprecated.

See https://github.com/NixOS/nixpkgs/commit/c71e2d42359f9900ea2c290d141c0d606471da16#commitcomment-21873221

* replace uses of lib.imap

* lib: move imap to deprecated.nix

lib/lists.nix

@@ -77,15 +77,21 @@ rec {
   */
   foldl' = builtins.foldl' or foldl;
 
-  /* Map with index
-
-     FIXME(zimbatm): why does this start to count at 1?
+  /* Map with index starting from 0
 
      Example:
-       imap (i: v: "${v}-${toString i}") ["a" "b"]
+       imap0 (i: v: "${v}-${toString i}") ["a" "b"]
+       => [ "a-0" "b-1" ]
+  */
+  imap0 = f: list: genList (n: f n (elemAt list n)) (length list);
+
+  /* Map with index starting from 1
+
+     Example:
+       imap1 (i: v: "${v}-${toString i}") ["a" "b"]
        => [ "a-1" "b-2" ]
   */
-  imap = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
+  imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
 
   /* Map and concatenate the result.