Move tests from parser.rs to appropriate parse_XX tests

[alamb]

Follow on to @ankrgyl 's suggestion in https://github.com/sqlparser-rs/sqlparser-rs/pull/842/files#r1149575835

I tried to clean up the tests a little both to make the current code a little nicer but also to help future contributors find the right place (and the right pattern)

[alamb]

I moved this code to sqlparser_common and sqlparser_mysql as appropriate, and used more concise functions to test these dialects

[alamb]

this is postgres specific so moved to sqlparser_postgres

[alamb]

moved to sqlparser_postgres

[alamb]

these tests are postgres specific (test with generic dialect and postgres) so moved to sqlparser_postgres

[coveralls]

Pull Request Test Coverage Report for Build 4650441892

• 32 of 32 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 86.279%

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Totals
Change from base Build 4650329513:	-0.02%
Covered Lines:	13903
Relevant Lines:	16114

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💛 - Coveralls

[ankrgyl]

lgtm pending one question!

[ankrgyl]

Did we lose these tests? I see a mysql dialect test for offset but not one that touches the other dialects. Apologies if I missed it!

[alamb]

Good spot. I should have called this out explicitly -- this test was replicated and therefore redundant.

The pre-existing test in sqlparser_common.rs is almost identical:

sqlparser-rs/tests/sqlparser_common.rs

Lines 6092 to 6104 in 784a191

	let sql = "SELECT * FROM student LIMIT $1 OFFSET $2";
	let ast = dialects.verified_query(sql);
	assert_eq!(
	ast.limit,
	Some(Expr::Value(Value::Placeholder("$1".into())))
	);
	assert_eq!(
	ast.offset,
	Some(Offset {
	value: Expr::Value(Value::Placeholder("$2".into())),
	rows: OffsetRows::None,
	}),
	);

[alamb]

Thanks for the review @ankrgyl