Add support for Postgres LIKE operators

[gruuya]

While at present there is support for the Postgres regex matching operators (~, ~*, !~, !~*), there is no support for parsing their Postgres LIKE equivalents: https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-LIKE.

These are the same as the regex operators, except that single-tilde's are replaced with double-tilde chars (~~, ~~*, !~~, !~~*):

The operator ~~ is equivalent to LIKE, and ~~* corresponds to ILIKE. There are also !~~ and !~~* operators that represent NOT LIKE and NOT ILIKE, respectively. All of these operators are PostgreSQL-specific. You may see these operator names in EXPLAIN output and similar places, since the parser actually translates LIKE et al. to these operators.