Use information schema tables in BigQuery

[drewbanin]

Feature

Feature description

BigQuery recently added support for an INFORMATION_SCHEMA in beta at the time of this writing.

When these tables become more mature (and we're confident they won't change in breaking ways) dbt should make use of them instead of using the BQ API directly. This will help keep things consistent across adapters, and will likely help us delete a whole bunch of code

[drewbanin]

@beckjake this should be closed by #1881, yeah?

[beckjake]

I think so!