* Properly track isFile, isSymlink, isDirectory
These don't exhaust all the possibilities, so none of them should be
defined as "neither of the others".
* empty
This a complex boring PR that shifts around code (primarily) in cli/fs.rs and
cli/ops/fs.rs. The gain of this refactoring is to ease the way for #4188 and
#4017, and also to avoid some future development pain.
Mostly there is no change in functionality. Except:
* squashed bugs where op_utime and op_chown weren't using `resolve_from_cwd`
* eliminated the use of the external `remove_dir_all` crate.
* op_chmod now only queries metadata to verify file/dir exists on Windows (it
will already fail on Unix if it doesn't)
* op_chown now verifies the file/dir's existence on Windows like chmod does.
