Rewrite type_* macros to use built-in adapter capabilities

[jtcohen6]

Split out from #577 + #597

Describe the feature

In dbt-utils: Rewrite the type_* macros to use each adapter's Column object. Think about whether it makes sense to push these macro into dbt-core as well, as a sugarier interface over the underlying Python methods.

Potential follow-up work in core + plugins:

• Extend / correct Column types as needed (e.g. [CT-636] [Bug] Postgres unlimited varchar default to varchar(256) dbt-core#5238)
• [Refactoring] Reconcile / consolidate agate type conversion methods with Column class type translation

Describe alternatives you've considered

Leave current dbt_utils.type_* macros as they are

Additional context

Yes, database-specific!

Who will this benefit?

• People relying on a mixture of dbt_utils.type_* macros (their own model SQL / installed package code) and Column-object behavior built into dbt's handling for, e.g., column type expansion in incremental models. It'd be better if these both pulled from the same set of information.
• All of us, in the long run, by consolidating these types and keeping them more consistent

Are you interested in contributing this feature?

Yes!