Bug 1857512: use utf-8 encoding for mozversioncontrol VCS commands r=zeid

`mozversioncontrol` runs currently use `universal_newlines`, which
is an alias for `text`. This forces the command output file object
to be opened in text mode using the platform's default encoding. On
Windows the default encoding is usually a single-byte encoding such
as `cp-1252`, which can cause issues when parsing patches that include
multi-byte sequences. Add an `encoding` option to `_run` with `utf-8`
as the default option and change the `check_output` call to use it.
Callers can revert to the previous behaviour quite easily by setting
`encoding=None` if necessary.

Differential Revision: https://phabricator.services.mozilla.com/D190710

python/mozversioncontrol/mozversioncontrol/__init__.py

@@ -95,7 +95,7 @@ class Repository(object):
     def __exit__(self, exc_type, exc_value, exc_tb):
         pass
 
-    def _run(self, *args, **runargs):
+    def _run(self, *args, encoding="utf-8", **runargs):
         return_codes = runargs.get("return_codes", [])
 
         cmd = (str(self._tool),) + args
@@ -108,7 +108,10 @@ class Repository(object):
         else:
             try:
                 return subprocess.check_output(
-                    cmd, cwd=self.path, env=self._env, universal_newlines=True
+                    cmd,
+                    cwd=self.path,
+                    env=self._env,
+                    encoding=encoding,
                 )
             except subprocess.CalledProcessError as e:
                 if e.returncode in return_codes: