Copies a stringified representation of the source SV into the
destination SV. Automatically performs any necessary mg_get and
coercion of numeric values into strings. Guaranteed to preserve
-UTF-8 flag even from overloaded objects. Similar in nature to
+UTF8 flag even from overloaded objects. Similar in nature to
sv_2pv[_flags] but operates directly on an SV instead of just the
string. Mostly uses sv_2pv_flags to do its work, except when that
would lose the UTF-8'ness of the PV.