Make dmetaphone collation-aware

Make dmetaphone collation-aware

The dmetaphone() SQL function internally upper-cases the argument
string.  It did this using the toupper() function.  That way, it has a
dependency on the global LC_CTYPE locale setting, which we want to get
rid of.

The "double metaphone" algorithm specifically supports the "C with
cedilla" letter, so just using ASCII case conversion wouldn't work.

To fix that, use the passed-in collation and use the str_toupper()
function, which has full awareness of collations and collation
providers.

Note that this does not change the fact that this function only works
correctly with single-byte encodings.  The change to str_toupper()
makes the case conversion multibyte-enabled, but the rest of the
function is still not ready.

Reviewed-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://www.postgresql.org/message-id/108e07a2-0632-4f00-984d-fe0e0d0ec726%40eisentraut.org