delete unsupported Filesystem.JL_O_ flags

[vtjnash]

We should probably delete ASYNC, CLOEXEC, LARGEFILE, and RSYNC exports from our list of filesystem flags list, since we neither define nor support any of those either.

Also, it looks like O_PATH and O_TMPFILE are the only (linux-specific) ones we might pass through successfully, so we could put an asterisk next to those noting they are linux-only.

Finally, could we rename these to something a bit more sensible (with aliases to these), without the JL_ since of course this is Julia. Maybe call it Base.Filesystem.O_APPEND? or expand to OPEN_APPEND? or contract it to APPEND?

Originally posted by @vtjnash in #53247 (comment)

[vtjnash]

Also synchronize these to have the correct UV_FS_O flag values, and make sure they all have the correct (Uint32?) type