Address issue where mozjs source files get auto-formatted by the editor according to mongodb formatting rules.

Update mozjs scripts to import `.clang-format` files from the spidermonkey repo into the mozjs source directory. Everything in `src/third_party/mozjs/` is still ignored by the linter and by `bazel run format` (see `.gitattributes` for the exclude) since there are some unformatted files in this directory, but an editor's format-on-save will pick up the mozjs clang-format rules.

The goal is to have formatting rules be the same between the mongo and spidermonkey repos, so there are less formatting conflicts when editing files that are in both repos.