feat: model MySQL expression-first CONVERT syntax

[minleejae]

MySQL CONVERT(expression, type) is not represented by the existing CONVERT grammar, which primarily handles the SQL Server type-first form and character-set conversion with USING. Valid casts such as CONVERT(amount, DECIMAL(12,4)) therefore fail or are interpreted in the wrong argument order.

Replace the internal boolean syntax choice in TranscodingFunction with USING, TYPE_FIRST and TYPE_LAST variants, retaining the existing constructors and boolean accessors. Share its rendering with ExpressionDeParser so operand visitors and type mutations work consistently. Reuse ColDataType for lengths, precision and character-set clauses.

The MYSQL dialect selects expression-first parsing for ambiguous inputs such as CONVERT(value, CHAR). Default and SQLSERVER parsing retain the existing type-first precedence; callers processing ambiguous MySQL input should explicitly select Dialect.MYSQL. Regression coverage includes USING, SQL Server styles and TRY_CONVERT, nested conversions, NULL, parameters, type mutation and incomplete arguments.

Syntax reference: MySQL conversion functions.

Validation:

• Full Gradle check passed on Java 17, including grammar ambiguity, formatting, static analysis, coverage and the full test suite. JUnit XML totals: 7997 tests, 0 failures/errors, 25 skipped.
• MySQL 8.4.11: 20 cases (16 valid, 4 invalid). For all 16 valid cases, the original SQL, toString() output and StatementDeParser output executed successfully with matching query results or resulting schema state. Invalid inputs were rejected by the server.

[manticore-projects]

Thank you!