Presto: Add function to convert strings to title case.

[fredabood]

According to the Presto docs, there is not currently a function to convert a string to title case.

[mosabua]

The typical standard name of such a function is initcap(string) from what i can tell.

[electrum]

This can be done using regex_replace. There's an example in the documentation: https://prestosql.io/docs/current/functions/regexp.html

```sql
SELECT regexp_replace('new york', '(\w)(\w*)', x -> upper(x[1]) || lower(x[2]));
-- 'New York'

[mosabua]

Thats a good workaround. Imho it would be good to have an actual function initcap or so.