windows: avoid a bytes vs unicode crash reading passwords on py2 stable

windows: avoid a bytes vs unicode crash reading passwords on py2

This broke in 5b3513177f2b.  Specifically, after typing in the password on py2,
it would crash with:

    TypeError: putwch() argument 1 must be cannot convert raw buffers, not str

--- a/mercurial/windows.py	Sun Aug 01 10:54:03 2021 -0400
+++ b/mercurial/windows.py	Mon Aug 02 10:51:19 2021 -0400
@@ -200,20 +200,20 @@
     This shouldn't be called directly- use ``ui.getpass()`` instead, which
     checks if the session is interactive first.
     """
-    pw = ""
+    pw = u""
     while True:
         c = msvcrt.getwch()  # pytype: disable=module-attr
-        if c == '\r' or c == '\n':
+        if c == u'\r' or c == u'\n':
             break
-        if c == '\003':
+        if c == u'\003':
             raise KeyboardInterrupt
-        if c == '\b':
+        if c == u'\b':
             pw = pw[:-1]
         else:
             pw = pw + c
-    msvcrt.putwch('\r')  # pytype: disable=module-attr
-    msvcrt.putwch('\n')  # pytype: disable=module-attr
-    return encoding.strtolocal(pw)
+    msvcrt.putwch(u'\r')  # pytype: disable=module-attr
+    msvcrt.putwch(u'\n')  # pytype: disable=module-attr
+    return encoding.unitolocal(pw)
 
 
 class winstdout(object):