Support UTF8 encoding for DPB strings

[dyemanov]

Starting with Firebird v3, the native fbclient always passes isc_dpb_utf8_filename (even if it wasn't specified by user) and all DPB strings are encoded in UTF8. .NET provider, however, passes everything "as is" (using system encoding), similar to how FB 2.5 fbclient works. This may break monitoring if isc_dpb_process_name contains non-ASCII characters and server's locale is different from the client's one (example: CP1251 on the Windows client, UTF8 on the Linux server). It would be convenient to follow the fbclient logic -- i.e. always pass isc_dpb_utf8_filename (and transliterate all DPB strings accordingly) -- for protocol P13 and above.