icu72: init at 72.1

https://icu.unicode.org/download/72

pkgs/development/libraries/icu/72.nix

···
+import ./base.nix {
+  version = "72.1";
+  sha256 = "sha256-otLTghcJKn7VZjXjRGf5L5drNw4gGCrTJe3qZoGnHWg=";
+}

pkgs/top-level/all-packages.nix

···
   icu71 = callPackage ../development/libraries/icu/71.nix ({
     nativeBuildRoot = buildPackages.icu71.override { buildRootOnly = true; };
   });
+  icu72 = callPackage ../development/libraries/icu/72.nix ({
+    nativeBuildRoot = buildPackages.icu72.override { buildRootOnly = true; };
+  });
 
   icu = icu71;