snowflake: allow $$ delimited strings

[jmccarv]

Enable support for $$ delimited string literals in the snowflake driver.

This enables queries that would otherwise fail, like:

select $$Hello 'world';$$;

[kenshaw]

@jmccarv Thanks for the contribution, I'll add to the next release. I was not aware that Snowflake support $$ strings. Though from a quick reading it doesn't seem to support the $tag$ ... $tag$ style that PostgreSQL does.

[jmccarv]

@kenshaw Thanks for the quick response!

You're right about it not supporting the $tag$ style. I didn't see a way to enable $$ strings without also enabling $tag$ in the code, but I suppose it shouldn't hurt to enable it anyway.

For giggles I tested $tag in snowflake with my patched version of usql:

=> select $xx$hi;$xx$;
error: snowflake: 1003: SQL compilation error:
syntax error line 1 at position 10 unexpected '$hi'.

I think that's nicer than the current error:

=> select $xx$hi;$xx$;
error: snowflake: 1003: SQL compilation error:
syntax error line 1 at position 10 unexpected '$hi'.
error: snowflake: 1003: SQL compilation error:
syntax error line 1 at position 0 unexpected '$xx'.

[kenshaw]

Yeah, I agree -- the goal of usql is not to work perfectly with every database, just to, ya know, provide something like an easier time for people who are used to psql to work with every other database. It wasn't a barrier for me merging the PR, just was pointing it out. Quick -- someone go file a ticket on the Snowflake projects to get proper PostgreSQL tag support! (heh)