* 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.
27affde592