convert: correctly convert paths to UTF-8 for Subversion
The previous code using encoding.tolocal() only worked by chance in these
situations:
* The string is ASCII: The fast path was triggered and the string was returned
unmodified.
* The local encoding is UTF-8: The source and target encoding is the same.
* The string is not valid UTF-8 and the native encoding is ISO-8859-1: If the
string doesn’t decode using UTF-8, ISO-8859-1 is tried as a fallback. During
`hg convert`, the local encoding is always UTF-8. The irony is that in this
case, encoding.tolocal() behaves like what someone would expect the reverse
function, encoding.fromlocal(), to do.
When the locale encoding is ISO-8859-15, trying to convert a SVN repo `/tmp/a€`
failed before like this:
file:///tmp/a%C2%A4 does not look like a Subversion repository to libsvn version 1.14.0
The correct URL is `file:///tmp/a%E2%82%AC`.
Unlike previously (with the ISO-8859-1 fallback), decoding the path using the
locale encoding can fail. In this case, we have to bail out, as Subversion
won’t be able to do anything useful with the path.
#require black
$ cd $RUNTESTDIR/..
$ black --config=black.toml --check --diff `hg files 'set:(**.py + grep("^#!.*python")) - mercurial/thirdparty/**'`