UI patches: find Steam internals by signature, offline checker

Runtime patches no longer use webpack module ids or minified export
names, which change with every Steam UI build:

- modules/lib/finders.js: finder library (getWebpackRequire,
  findModule/findExport by source text and shape, resolveAll with a
  per-page cache, findFiberUp/findFiberDown/findInReactTree), installed
  once per page as window.__sfuiFind.
- modules/lib/signatures.json: the signatures, per patch, shared by the
  patches and the checker. lib/default.nix mkPatch wraps a patch
  `(find, sigs, opts) => ...` with the library, its signatures and
  options; exposed as steamFrame.uiPatches.lib.
- Keyboard patch (VERSION 10): layouts module, current/enabled layout
  getters, arrow keys, VR keyboard status and VirtualKeyboardManager are
  found by signature; if one doesn't match it reports which and leaves
  Steam untouched. unpatch.js uses references the patch remembered.
  The helper logs inject results when they change.
- launcher-menu launch/pinned-desktop use the library's fiber helpers;
  launch no longer depends on the bar popup's window name.
- scripts/check-signatures.mjs (+ webpack-modules.mjs): extracts module
  factories from the installed bundles without a browser and checks
  every signature (found / ambiguous / missing, with module ids and
  export names). README: "Finders and signatures", "After a Steam update".

modules/steam-keyboard-patch.nix

@@ -11,8 +11,17 @@
 #   performs those requests with xdotool on :0 (X focus follows the window
 #   selected in VR) and reverts the patch when stopped (unpatch.js). Its
 #   allowlist can't type ASCII text or press Enter.
-# Depends on Steam UI internals; tested with Steam client 1790377368.
-{ config, pkgs, lib, ... }: {
+# Depends on Steam UI internals, found by signature (lib/finders.js, entry
+# "steam-keyboard-patch" in lib/signatures.json) rather than webpack module
+# ids; after a Steam update, scripts/check-signatures.mjs tells whether they
+# still match. Tested with Steam client 1790377368 (UI build 11041156).
+{ config, pkgs, lib, ... }:
+let
+  patch = (import ./lib { inherit pkgs; }).mkPatch {
+    name = "steam-keyboard-patch";
+    src = ./steam-keyboard-patch/patch.js;
+  };
+in {
   imports = [ ./session.nix ];
 
   options.steamFrame.steamKeyboardPatch.enable = lib.mkEnableOption ''
@@ -31,7 +40,7 @@
         ExecStart = lib.escapeShellArgs [
           "${pkgs.nodejs}/bin/node"
           "${./steam-keyboard-patch/helper.mjs}"
-          "${./steam-keyboard-patch/patch.js}"
+          "${patch}"
           "${./steam-keyboard-patch/unpatch.js}"
           "${pkgs.xdotool}/bin/xdotool"
         ];