Support PostgreSQL tagged dollar strings and preserve literal bodies

[minleejae]

Tagged PostgreSQL strings such as $json$…$json$ currently fail to parse or become column references. Recognize them as StringValue while preserving the exact delimiter, whitespace and literal contents:

SELECT $json$[{"some":"json","with":"properties$"}]$json$::jsonb;

Reuse a shared delimiter recognizer in the lexer, StringValue and routine-body boundary detection. The lexer reads the original character stream with a linear delimiter matcher, handles longest-match identifier tokens, and updates token end positions. Dollar-quoted values keep doubled apostrophes unchanged in getNotExcapedValue(). A tagged routine body remains one token, so a following SQL statement is preserved.

Tagged quoting is enabled by default. For dialects that use the same spelling as an unquoted identifier, withDollarQuotedStringTags(false) preserves the previous identifier interpretation; ordinary dollar-containing identifiers, positional parameters and untagged $$ literals remain supported.

Validation:

• Full Gradle check and Maven verify.
• Re-enabled the existing tagged-string regression test.
• Empty/Unicode tags, whitespace and CRLF preservation, embedded dollar signs and other tags, casts, bind parameters, quoted identifiers and the compatibility option.
• Model/deparser round-trips, token positions, long Reader/InputStream inputs with overlapping delimiter prefixes, unterminated tags, and routine bodies followed by another statement.
• Syntax follows the PostgreSQL dollar-quoting documentation.

Fixes #2233.