Accept named FOREIGN KEY and CHECK drops without a dialect

[minleejae]

Purpose

Parse ALTER TABLE t DROP FOREIGN KEY fk and ALTER TABLE t DROP CHECK ck without selecting a dialect. These common MySQL actions fail in the default configuration, as reported in #990 and #1129. Dialect.MYSQL has accepted them since #2675.

Current design (As-is)

The named form is selected only when the dialect is MYSQL:

• Without a dialect, only the legacy parenthesized DROP FOREIGN KEY (cols) form is accepted.
• Dialect.MARIADB also rejects DROP FOREIGN KEY fk, although MariaDB supports it.

Target design (To-be)

• Without a dialect, accept the named FOREIGN KEY and CHECK drops, exactly as with Dialect.MYSQL.
• With Dialect.MARIADB, accept the named FOREIGN KEY drop. MariaDB has no DROP CHECK, so that form stays rejected.
• Keep rejecting both in other dialects, which drop constraints with DROP CONSTRAINT.
• A parenthesized FOREIGN KEY column list keeps the legacy form.
• The AST is unchanged: DROP_FOREIGN_KEY/DROP_CHECK with getConstraintName().
• Update the usage guide.

Validation

• 8 new tests cover:
  • default-mode round trips with plain and quoted names, including the combined DROP FOREIGN KEY fk1, DROP CHECK c1;
  • MariaDB acceptance and rejection;
  • rejection in the PostgreSQL, Oracle and SQL Server dialects;
  • the legacy parenthesized form.
• Java 17 offline Gradle spotlessApply check: 10,102 tests, 10,077 passed, 25 skipped, zero failures/errors. The grammar choice conflict check passes.
• Database runs, with SQL rendered both without a dialect and with the server's dialect:
  • MySQL 8.4 and 8.0: 4 statements each succeed in original and rendered form.
  • MariaDB 11.4: DROP FOREIGN KEY fk1 succeeds; DROP CHECK c1 is rejected by both the server and the parser in MariaDB mode.
  • PostgreSQL 18.3: the named FOREIGN KEY drop is rejected by both.

Integration validation

Applied #2788, #2789, #2790, #2791 and #2792 together on master (166f0a27):

• Every pair merges without conflicts, and the combined grammar is free of choice conflicts.
• The integrated build passes Java 17 offline Gradle spotlessApply check: 10,150 tests, 10,125 passed, 25 skipped, zero failures/errors.
• With the integrated build, the same server results hold on MySQL 8.4, MySQL 8.0, MariaDB 11.4 and PostgreSQL 18.3:
  • the 95 statement cases of these PRs;
  • the 11 default-mode drop cases;
  • 51 string literal comparisons, including 16 mixed-escape literals that need Lex MySQL backslash escapes consistently in string literals #2790 and Resolve backslash escapes in StringValue.getNotExcapedValue() #2791 together.