git-p4: fix CR LF handling for utf16 files

Perforce silently replaces LF with CR LF for "utf16" files if the client
is a native Windows client. Since git's autocrlf logic does not undo
this transformation for UTF-16 encoded files, git-p4 replaces CR LF with
LF during the sync if the file type "utf16" is detected and the Perforce
client platform indicates that this conversion is performed.

Windows only runs on little-endian architectures, therefore the encoding
of the byte stream received from the Perforce client is UTF-16-LE and
the relevant byte sequence is 0D 00 0A 00.

Signed-off-by: Moritz Baumann <moritz.baumann@sap.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -3148,7 +3148,7 @@ class P4Sync(Command, P4UserMap):
                     raise e
             else:
                 if p4_version_string().find('/NT') >= 0:
-                    text = text.replace(b'\r\n', b'\n')
+                    text = text.replace(b'\x0d\x00\x0a\x00', b'\x0a\x00')
                 contents = [text]
 
         if type_base == "apple":