fix(redshift)!: Normalize time units in their full singular form

[VaggelisD]

Fixes #3651

Normalize Redshift's units from plural/abbreviation to their full singular form during parse time. This is already happening at Snowflake, so the existing infrastructure is moved out to dialect.py as most of these mappings are similar between dialects.

[VaggelisD]

I thought again and have concluded to the following regarding this PR:

• I moved DATE_PART_MAPPING to Dialect, thus any dialect that wants to change it's mappings can do so and pass its self in map_date_part().
• There was a dispute between Redshift EPOCH & Snowflake EPOCH_SECOND but Snowflake also supports EPOCH, EPOCH_SECONDS as abbreviations for EPOCH_SECOND; Thus, I followed the convention that Snowflake will turn EPOCH_SECOND -> EPOCH, and with this change we won't need to override the mapping in either dialect

Regarding the general refactor:

• We can probably swap exp.TimeUnit::UNABBREVIATED_UNIT_NAME with Dialect::DATE_PART_MAPPING, which should normalize most (if not all) dialects and remove the need for map_date_part() everywhere.
• If any dialect has different mappings, we can go the manual map_date_part(unit, dialect) route. This is a necessary evil because exp.TimeUnit won't have access to the dialect specific mapping, but we can rethink this later on.

Any thoughts?

Redshift date parts | Snowflake date parts

[georgesittas]

LGTM

We can probably swap exp.TimeUnit::UNABBREVIATED_UNIT_NAME with Dialect::DATE_PART_MAPPING, which should normalize most (if not all) dialects and remove the need for map_date_part() everywhere.

Sounds good. If there are no inconsistencies between dialects then that would make things simpler. The tricky part begins when you have to override certain date parts because there are discrepancies.

If any dialect has different mappings, we can go the manual map_date_part(unit, dialect) route. This is a necessary evil because exp.TimeUnit won't have access to the dialect specific mapping, but we can rethink this later on.

Right, so we'll be able to have an escape hatch. Sounds good to me 👍