Support SQL Server typed XML schema collections

[minleejae]

Fixes #1567

Changes

• Support SQL Server typed XML with optional CONTENT/DOCUMENT and one- or two-part XML schema collection names, including quoted identifiers.
• Model the modifier as an immutable XmlTypeModifier, separately from numeric type arguments. Preserve omission of the facet and expose its effective CONTENT default.
• Reuse the datatype production in CREATE TABLE, ALTER TABLE, and DECLARE. Keep schema collection names out of table discovery.
• Include the modifier in ColDataType equality/hashCode and correct the existing case-insensitive equality/hash mismatch, including Unicode case folding.

Verification

• Full Gradle check (tests, Checkstyle, PMD, Spotless).
• Maven clean verify with Java 17.
• The complete CREATE TABLE example from Failed to parse SQL Server ddl #1567, round-trip and malformed-type tests, untyped XML/numeric datatype regressions, and immutable-value/equality tests.

Reference: SQL Server xml datatype.