use lookup paths in helper expressions consistently

this makes the files in question a bit more independent of source location.

to find where the value is set and how it's wired up:

    rg nix=doc/manual

doc/manual/generate-builtin-constants.nix

@@ -1,6 +1,6 @@
 let
   inherit (builtins) concatStringsSep attrValues mapAttrs;
-  inherit (import ./utils.nix) optionalString squash;
+  inherit (import <nix/utils.nix>) optionalString squash;
 in
 
 builtinsInfo:

doc/manual/generate-builtins.nix

@@ -1,6 +1,6 @@
 let
   inherit (builtins) concatStringsSep attrValues mapAttrs;
-  inherit (import ./utils.nix) optionalString squash;
+  inherit (import <nix/utils.nix>) optionalString squash;
 in
 
 builtinsInfo:

doc/manual/generate-manpage.nix

@@ -1,9 +1,29 @@
 let
   inherit (builtins)
-    attrNames attrValues fromJSON listToAttrs mapAttrs groupBy
+    attrNames
-    concatStringsSep concatMap length lessThan replaceStrings sort;
+    attrValues
-  inherit (import <nix/utils.nix>) attrsToList concatStrings optionalString filterAttrs trim squash unique;
+    concatMap
-  showStoreDocs = import ./generate-store-info.nix;
+    concatStringsSep
+    fromJSON
+    groupBy
+    length
+    lessThan
+    listToAttrs
+    mapAttrs
+    match
+    replaceStrings
+    sort
+    ;
+  inherit (import <nix/utils.nix>)
+    attrsToList
+    concatStrings
+    filterAttrs
+    optionalString
+    squash
+    trim
+    unique
+    ;
+  showStoreDocs = import <nix/generate-store-info.nix>;
 in
 
 inlineHTML: commandDump:

doc/manual/generate-settings.nix

@@ -1,6 +1,6 @@
 let
   inherit (builtins) attrValues concatStringsSep isAttrs isBool mapAttrs;
-  inherit (import ./utils.nix) concatStrings indent optionalString squash;
+  inherit (import <nix/utils.nix>) concatStrings indent optionalString squash;
 in
 
 # `inlineHTML` is a hack to accommodate inconsistent output from `lowdown`

doc/manual/generate-store-info.nix

@@ -1,7 +1,7 @@
 let
   inherit (builtins) attrValues mapAttrs;
-  inherit (import ./utils.nix) concatStrings optionalString;
+  inherit (import <nix/utils.nix>) concatStrings optionalString;
-  showSettings = import ./generate-settings.nix;
+  showSettings = import <nix/generate-settings.nix>;
 in
 
 inlineHTML: storesInfo:

doc/manual/generate-xp-features-shortlist.nix

@@ -1,5 +1,5 @@
 with builtins;
-with import ./utils.nix;
+with import <nix/utils.nix>;
 
 let
   showExperimentalFeature = name: doc:

doc/manual/generate-xp-features.nix

@@ -1,5 +1,5 @@
 with builtins;
-with import ./utils.nix;
+with import <nix/utils.nix>;
 
 let
   showExperimentalFeature = name: doc: