Fix implementation of Snowflake's TO_TIME/TO_TIMESTAMP functions

[vil1]

Improve the way TO_TIME and TO_TIMESTAMP are translated.

• When called with an explicit format, said format is properly translated (for instance, SF's format YYYY-MM-DD HH24:MITZH:TZM gets translated into DB's yyyy-MM-dd'T'HH:mmZZZ), be it a constant or a variable.
• When SF's TO_TIMESTAMP is called with the TO_TIMESTAMP ( <numeric_expr> , <scale> ) we simply truncate numeric_expr to a number-of-seconds-since-epoch, as it seems to be the best we can do.
• When TO_TIMESTAMP is called with no explicit format, we do our best as to handle the automatic formats that SF handles but DB doesn't by trying each explicitly until one matches
• the DY format part (corresponding to EEE in DB), ie. day-of-week, isn't allowed anymore since Spark 3.0. Since it isn't relevant in figuring out a specific point in time, we simply ignore it in both translated format and input string (resulting in huge amount of SQL being produced, see tests/resources/functional/snowflake/core_engine/functions/conversion/to_timestamp_variable_format.sql for an example)

[github-actions[bot]]

Coverage tests results

456 tests  +1   419 ✅ +1   4s ⏱️ ±0s   6 suites ±0    37 💤 ±0    6 files   ±0     0 ❌ ±0 

Results for commit e05db34b. ± Comparison against base commit 0f06d166.

This pull request removes 9 and adds 10 tests. Note that renamed tests count towards both.

``` com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/conversion/test_to_time/test_to_time_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/conversion/test_to_time/test_to_time_2.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/conversion/test_try_to_date/test_try_to_date_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/conversion/test_try_to_date/test_try_to_date_3.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/conversion/to_timestamp_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/dates/dayname/test_dayname_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/dates/monthname/test_monthname_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/dates/test_date_trunc_2.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ functions/dates/test_date_trunc_3.sql ``` ``` com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/test_to_time_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/test_to_time_2.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/test_try_to_date_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/test_try_to_date_3.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/to_timestamp_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/conversion/to_timestamp_variable_format.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/dates/test_date_trunc_2.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/dates/test_date_trunc_3.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/dates/test_dayname_1.sql com.databricks.labs.remorph.coverage.SnowflakeAcceptanceSuite ‑ core_engine/functions/dates/test_monthname_1.sql ```

:recycle: This comment has been updated with latest results.