Fix ldap search with binary values

[CravateRouge]

\\XX (XX being an hex value) in ldap query string value was re-decoded in the query string using chr(\xXX) by calling _read_EscapedCharacter -> _read_ASCII_VALUE -> _read_HEX_VALUE.

However chr() interprets \xXX as a unicode code point U+00XX but for example U+00a0 has a binary representation of \xC2\xA0. Hence, the current parser doesn't correctly handle the encoding of the \\XX bytes provided by the user and the binary search cannot be used because it sends a wrong binary representation to the server.

To comply with RFC 4515 specifying that the notation \\XX can be used to search for binary values, I disabled the re-encoding part detected by if chunk0 == '\\' l.1263 in msldap/protocol/ldap_filter/parser.py and instead called a special encoding function called RFC4515_encode() when encoding the string into the asn1 structure. The encoding function cannot be called before (e.g. instead of _read_HEX_VALUE) because not all bytes have a string representation in UTF8 and for example b'\xa0'.decode() will fail and as stated previously chr(\xa0) will not give the right decoding of our binary value.

With this PR, you'll be able to perform queries such as this one:

guid_str = "\\" + "\\".join([
                "{:02x}".format(b)
                for b in dtyp.guid.GUID().from_string('2628A46A-A6AD-4AE0-B854-2B12D9FE6F9E').to_bytes()
            ])
    filter = f"(schemaIDGUID={guid_str})"
connection.pagedsearch(query= f"(schemaIDGUID={guid_str})", attributes=attributes, tree=dn)

'2628A46A-A6AD-4AE0-B854-2B12D9FE6F9E' being the schemaIDGUID for CN=account,CN=Schema,CN=Configuration,DC=your,DC=domain

[skelsec]

Awesome! Thank you!