[FEATURE] dialect presets for the lexer-level feature switches

[fudianchn]

AI disclosure: this issue was prepared with AI coding agents, reviewed and revised line by line by me.

Grammar or Syntax Description

Not a single grammar production, but the switch layer below it. JSqlParser now has three lexer-level switches, each added when one lexeme carries different meanings in two dialects:

• Feature.allowSquareBracketQuotation (v3.0, should bracket quotation (like sqlserver supports it) be removed to be able to support array constructs #677: SQL Server quoting vs Postgres arrays)
• Feature.allowBackslashEscapeCharacter (v4.6: backslash escapes)
• Feature.allowHashLineComments (feat(parser): support MySQL # line comments behind allowHashLineComments #2508: MySQL # line comments vs the Postgres # operator from fix(parser): support PostgreSQL # binary operator (bitwise XOR / geometric intersection) #2507)

Every lexeme conflict settled the same way adds one more switch, and every user of a dialect then has to know and wire the full set by hand:

CCJSqlParserUtil.parse(sql, parser -> parser.withBackslashEscapeCharacter(true)
        .withHashLineComments(true));

Proposal: a preset layer so one call selects the dialect's full switch set. Prototyping found the parser already owns a narrow Dialect enum (ORACLE, EXASOL) behind withDialect(Dialect) for grammar gating, so extending that enum keeps a single entry point:

CCJSqlParserUtil.parse(sql, parser -> parser.withDialect(Dialect.MYSQL));

Pure data mapping, no mechanism changes: individual switches keep working and override the preset.

SQL Example

One statement, MySQL reading, today vs proposed:

-- MySQL: `col` is a quoted identifier, 'x\'yz' keeps the escaped quote, 42#24 is 42 plus a line comment
SELECT `col` FROM t WHERE a = 'x\'yz' AND b = 42#24

today: two switches wired manually per parse call (backticks already parse by default, brackets are not MySQL syntax); proposed: withDialect(Dialect.MYSQL) once.

Additional context

• Current master 177dbd7.
• Follow-up sketched at the end of feat(parser): support MySQL # line comments behind allowHashLineComments #2508: "The dialect presets sketched in the fix: support MySQL # line comments (#2499) #2502 discussion would be a small standalone follow-up if you want them: a mapping from DatabaseType to the existing Feature set, no mechanism changes."
• fix: support MySQL # line comments (#2499) #2502 holds the full history of the one-lexeme-two-dialects class of problem (square brackets, backslash, #).
• Open design points: which switches each preset turns on (POSTGRESQL may need none, since the defaults already follow the PG reading), whether the mapping lives on the parser's Dialect enum or beside the validation-side DatabaseType, and whether the validation feature sets and the parse-time switches should share one table.
• feat(parser): turn on the dialect's lexer feature preset in withDialect #2511 answers the first two points (empty presets for the PG-default dialects, mapping on the parser's Dialect enum); the shared validation table stays open as a follow-up.