This commit fixes a bunch of issues at the same time, as they are all
related to path handling:
- `pathlib.Path.resolve()` or `.absolute()` are replaced by
`bpathlib.make_absolute()`. The latter does NOT follow symlinks and does
NOT network mounts from a drive letter to UNC notation. This also has
advantages on non-Windows sytems, as it allows BAT-packing a directory
structure with symlinked files (such as a Shaman checkout).
- Better handling of drive letters, and of paths that cross drive
boundaries.
- Better testing of Windows-specific cases when running the tests on
Windows, and of POSIX-specific cases on other platforms.
Thanks to @wisaac for starting this patch in D6676.
Thanks to @jbakker for pointing out the drive letter issue. This fixes
T70655.
The target path is just read as string from the CLI now, to allow more
complex targets (such as URLs) that don't directly map to a path.
The Packer subclass now handles the conversion from that string to a
`pathlib.PurePath`, and specific subclasses & transfer classes can convert
those to a `pathlib.Path` to perform actual filesystem operations when
necessary.
