[CT-456] Make internal macros use macro dispatch to be overridable in child adapters.

[ueshin]

Describe the feature

A child adapter, e.g., dbt-databricks, wants to override the internal macros for creating table, such as file_format_clause, options_clause, but currently it's unclear whether they are overridable or not.
We should explicitly use macro dispatch mechanism.

Describe alternatives you've considered

Just use the same macro names, but it's not clear whether the proper macros will be used.

Additional context

The discussion is databricks/dbt-databricks#72 (comment)

Who will this benefit?

For a child adapter maintainers to make sure they can override the macros.

Are you interested in contributing this feature?

Yes.

[jtcohen6]

@ueshin Thanks for opening the issue + PR!