[fix] use cast macro in default__get_empty_schema_sql

[MichelleArk]

resolves #166
docs dbt-labs/docs.getdbt.com/#

Problem

adapter-specific cast macro not being used in default__get_empty_schema_sql which leads to adapter-specific cases being mishandled and erroring.

Solution

Use the newly available adapter-specific cast macro! By default, this is just a refactor since the default implementation just does a cast <field> as <type>. However, adapters that override the cast macro (e.g. snowflake) would benefit from broader type support in constraint enforcement if the base implementation of get_empty_schema_sql made use of the adapter-specific override.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development, and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
  • Snowflake tests: test constraints for geometry and geography types dbt-snowflake#969
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX

🎩

-- geography.sql
SELECT 
TO_GEOMETRY('POINT(1820.12 890.56)') as geometry_field, 
TO_GEOGRAPHY('POINT(-122.35 37.55)') as geography_field

✅ correct & passing contract:

❯ dbt run --select geography
02:05:28  Running dbt...
02:05:28  target not specified in profile 'snowflake', using 'default'
02:05:29  Found 14 models, 6 seeds, 20 data tests, 6 sources, 13 metrics, 709 macros, 6 semantic models, 3 unit tests
02:05:29  
02:05:31  Concurrency: 4 threads (target='default')
02:05:31  
02:05:31  1 of 1 START sql view model dbt_marky.geography ................................ [RUN]
02:05:31  1 of 1 OK created sql view model dbt_marky.geography ........................... [SUCCESS 1 in 0.72s]
02:05:31  
02:05:31  Finished running 1 view model in 0 hours 0 minutes and 1.84 seconds (1.84s).
02:05:31  
02:05:31  Completed successfully
02:05:31  
02:05:31  Done. PASS=1 WARN=0 ERROR=0 SKIP=0 TOTAL=1

✅ incorrect and failing contract error message looks good!

❯ dbt run --select geography
02:06:46  Running dbt...
02:06:46  target not specified in profile 'snowflake', using 'default'
02:06:47  Found 14 models, 6 seeds, 20 data tests, 6 sources, 13 metrics, 709 macros, 6 semantic models, 3 unit tests
02:06:47  
02:06:48  Concurrency: 4 threads (target='default')
02:06:48  
02:06:48  1 of 1 START sql view model dbt_marky.geography ................................ [RUN]
02:06:49  1 of 1 ERROR creating sql view model dbt_marky.geography ....................... [ERROR in 0.70s]
02:06:49  
02:06:49  Finished running 1 view model in 0 hours 0 minutes and 1.80 seconds (1.80s).
02:06:49  
02:06:49  Completed with 1 error and 0 warnings:
02:06:49  
02:06:49    Compilation Error in model geography (models/geography.sql)
  This model has an enforced contract that failed.
  Please ensure the name, data_type, and number of columns in your contract match the columns in your model's definition.
  
  | column_name     | definition_type | contract_type | mismatch_reason    |
  | --------------- | --------------- | ------------- | ------------------ |
  | GEOGRAPHY_FIELD | GEOGRAPHY       | TEXT          | data type mismatch |
  | GEOMETRY_FIELD  | GEOMETRY        | TEXT          | data type mismatch |

[github-actions]

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[dbeatty10]

@MichelleArk looks like the combination of this PR and dbt-labs/dbt-snowflake#969 resolves dbt-labs/dbt-snowflake#894 too 🤩