* remove deprecated `std.fs.Dir` APIs
 * `std.fs.Dir.openDir` now takes a options struct with bool fields for
   `access_sub_paths` and `iterate`. It's now much more clear how
   opening directories works.
 * fixed the std lib and various zig code calling the wrong openDir
   function.
 * the runtime safety check for dir flags is removed in favor of the
   cheaper option of putting a comment on the same line as handling
   EBADF / ACCESS_DENIED, since that will show up in stack traces.