Support Informix trailing constraint names and share constraint rendering

[minleejae]

Informix places an optional constraint name after its definition, for example:

ALTER TABLE child ADD CONSTRAINT FOREIGN KEY (id)
REFERENCES parent(id) CONSTRAINT fk_child;

Support this form for primary, unique, foreign and check constraints, including unnamed constraints, when explicitly selecting parser.withDialect(Dialect.INFORMIX). Other dialects retain the existing constraint interpretation.

The existing constraint models expose the name, columns, referenced table and CHECK expression; NamedConstraint.ConstraintNamePosition preserves the name's placement. Shared prefix/suffix rendering keeps model and deparser output consistent while preserving the existing leading-name API defaults.

Validation:

• Full Gradle check and Maven verify.
• Original primary/foreign/unique reproducers, quoted and omitted names, composite keys, mutable AST names, subsequent actions/statements, malformed input, and rejection of trailing names without the Informix dialect.
• SQL round-trips, CHECK expression visitor customization, referenced-table traversal, and existing CREATE/ALTER regression tests.
• Syntax checked against the Informix ADD CONSTRAINT documentation.

Fixes #271.

[manticore-projects]

Thank you much!