Support mssql json and xml extensions

[lovasoa]

Adds support for SQL syntax like

SELECT * FROM t FOR JSON PATH, ROOT('x'), INCLUDE_NULL_VALUES
SELECT * FROM t FOR XML PATH('x'), ROOT('y'), ELEMENTS

fixes #1042

See the documentation for the FOR clause here: https://learn.microsoft.com/en-us/sql/t-sql/queries/select-for-clause-transact-sql?view=sql-server-ver16

[coveralls]

Pull Request Test Coverage Report for Build 6910265870

• 175 of 184 (95.11%) changed or added relevant lines in 7 files are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.07%) to 87.715%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/query.rs	52	56	92.86%
src/parser/mod.rs	80	85	94.12%

Files with Coverage Reduction	New Missed Lines	%
src/lib.rs	5	11.83%

Totals
Change from base Build 6829537554:	0.07%
Covered Lines:	17786
Relevant Lines:	20277

---

💛 - Coveralls

[lovasoa]

@alamb : I'd love to get your feedback on this. I'm adding more JSON-related features to SQLPage, and missing json support is blocking for mssql users.

I also added support for the XML syntax while I was at it.

[alamb]

Thanks @lovasoa - I hope to find time to review this over the next few days

[lovasoa]

@alamb , did you find the time to give a quick look ? I'd like to release a new version of sqlpage with this :)

[alamb]

Looks good to me -- thank you @lovasoa

[lovasoa]

Great, thank you @alamb !