Tweak profile directory layout

doom-profile-data-dir is for the current profile, naming it
"profiles" (plural) made no sense.

Also move the loader into its own subdir so it's more obvious what the
two init.29.elc files are.

doom.nix

@@ -269,11 +269,12 @@ let
 
     echo '
     ((${profileName} (user-emacs-directory . "${doomSource}")
-        (doom-profile-data-dir . "'$out'/profiles")
+        (doom-profile-data-dir . "'$out'/profile")
         ("DOOMDIR" . "${finalDoomDir}")))
     ' > profiles.el
 
-    export DOOMPROFILELOADFILE=$out/init.el
+    mkdir $out/loader
+    export DOOMPROFILELOADFILE=$out/loader/init.el
     export DOOMPROFILELOADPATH=$PWD/profiles.el
     export DOOMLOCALDIR=$(mktemp -d)
     # Prevent error on Emacs shutdown writing empty build cache.
@@ -301,7 +302,7 @@ let
   }
   ''
   makeWrapper ${emacsWithPackages}/bin/emacs $out/bin/emacs \
-    --set DOOMPROFILELOADFILE ${doomProfile}/init.el \
+    --set DOOMPROFILELOADFILE ${doomProfile}/loader/init.el \
     --add-flags "--init-directory=${doomSource} --profile ${profileName}"
 '';