fs: fix `fs.openAsBlob`, add `fs.openAsBlobSync` and `fsPromises.openAsBlob`
fs.openAsBlob()
was added in https://github.com/nodejs/node/pull/45258 as part of Callback API despite returning Promise instead of calling callback.
I guess it should look more like this?
https://github.com/nodejs/node/labels/semver-minor unless there are objections (fs.openAsBlob
was marked as experimental).
cc @jasnell