kodi: copy web assets instead of symlinking

Kodi refuses to follow symlinks that lead outside of a small whitelist
of allowed directories. See
[`CFileUtils::CheckFileAccessAllowed`](https://github.com/xbmc/xbmc/blob/4ac445c4a9f3080895bfcc34e7115e2de5b66d22/xbmc/utils/FileUtils.cpp#L252)
for the relevant code.

This feels like a pretty brittle workaround, but I can't think of a
better solution, so I'm going to say that this fixes
https://github.com/NixOS/nixpkgs/issues/145116.

pkgs/applications/video/kodi/wrapper.nix

@@ -35,5 +35,11 @@ buildEnv {
           (lib.concatMap
             (plugin: plugin.extraRuntimeDependencies or []) addons)}"
     done
+
+    # makeWrapper just created webinterface.default as a symlink. However,
+    # kodi's webserver carefully refuses to follow symlinks, so we need to copy
+    # these assets instead.
+    rm $out/share/kodi/addons/webinterface.default
+    cp -r ${kodi}/share/kodi/addons/webinterface.default/ $out/share/kodi/addons/webinterface.default
   '';
 }