feat: support MySQL JSON_TABLE column collations

[minleejae]

MySQL JSON_TABLE accepts column definitions such as n VARCHAR(10) COLLATE utf8mb4_bin PATH '$.n', but the parser stops at COLLATE. Parse an optional collation after the column type when Dialect.MYSQL is selected.

Expose the collation through JsonTableValueColumnDefinition.getCollation()/setCollation(String), preserve quoting, and render it with the column. Users can inspect, replace, remove or construct a collation without editing SQL strings. Character-set information remains in the existing ColDataType.

Validation: ./gradlew check passed. Tests cover bare, backtick-quoted and string-quoted collation names, an explicit character set, nested columns, AST construction and edits, both renderers, reparsing and dialect boundaries. Six SELECT/CREATE TABLE AS reproductions were executed on MySQL 8.4.11 before and after rendering, with identical results.

Collated EXISTS columns also need the existing EXISTS output-order correction in #2682; the changes are kept in separate PRs and tested together.

Reference: MySQL JSON_TABLE typed columns.

Combined validation with #2682, #2683, #2684, #2685 and #2686: all five changes merge without conflicts; the integrated ./gradlew check passes (8,190 tests, 25 skipped). All 254 MySQL 8.4.11 fixtures parse, render and reparse, and execute with results identical to the original SQL.