Support more DateTimeField variants

[iffyio]

• Adds DATETIME variant to DatetimeField
• Adds support for snowflake abbreviations via Custom variant. https://docs.snowflake.com/en/sql-reference/functions-date-time#supported-date-and-time-parts
• Adds support for BigQuery weekday WEEK(MONDAY) syntax https://cloud.google.com/bigquery/docs/reference/standard-sql/date_functions#extract

[coveralls]

Pull Request Test Coverage Report for Build 8407785234

Details

• 77 of 86 (89.53%) changed or added relevant lines in 6 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.01%) to 87.882%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/mod.rs	12	13	92.31%
tests/sqlparser_bigquery.rs	9	10	90.0%
src/ast/value.rs	39	46	84.78%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_common.rs	3	97.14%

Totals
Change from base Build 8266982631:	0.01%
Covered Lines:	20524
Relevant Lines:	23354

---

💛 - Coveralls

[alamb]

Thank you @iffyio (and I very much apologize for the delay in reviewing). The only thing I think this PR needs is to avoid creating intermediate strings in the Display fmt

[alamb]

This change to call to_string() will now cause a new string to be allocated for each type.

I think it would be better / more effiicent to use write! directly -- like

Suggested change

	DateTimeField::Year => "YEAR".to_string(),
	match self {
	DateTimeField::Year => f.write_str("YEAR"),
	DateTimeField::Month => f.write_str("MONTH"),
	...

[iffyio]

Ah yes that makes a lot more sense, thanks for the follow up fix too!

[alamb]

(for anyone following along it was #1209)

[alamb]

If you use the suggestion below I think you will not need these imports either

[alamb]

In order to keep the code flowing (and the fact it took me so long to review this PR) I fixed the string copy issue and pushed a fix to this PR.

Thanks again @iffyio