Use show schemas instead of selecting from information_schema.schemata on Snowflake

[drewbanin]

Describe the feature

Background:

Let's replace the call to information_schema.schemata on Snowflake with a call to show schemas in <database>.

Advantages:

• show schemas will not queue, whereas the select statement can queue
• show schemas does not require a running warehouse
• show schemas appears to be strictly faster than the information_schema alternative

We should consider applying this approach for other queries, as described in #1877 (the key benefit being that these queries do not queue. Let's keep #1877 open and tackle these other queries separately. See also #2157

Disadvantages:

• show schemas requires the database name to be cased and quoted appropriately. I actually think this is the same behavior as selecting from database.information_schema.<table>, so that might not be an issue here?

[beckjake]

The big drawback of show schemas is that it has a 10,000 record limit, so users with 10k schemas in their database (and I assume those users do exist!) will have problems. We can either fail if there are 10k or fall back to querying information_schema.schemata. I'd really rather error out, but I understand the appeal of falling back.