clickhouse-jdbc (v1): the JavaCC SQL parser has no heredoc token, so a ; inside $$...$$ truncates the statement #3039

Describe the bug

The legacy clickhouse-jdbc (v1) JavaCC grammar
(clickhouse-jdbc/src/main/javacc/ClickHouseSqlParser.jj) has no heredoc token, so the body of a
ClickHouse heredoc literal ($$body$$ / $tag$body$tag$) is lexed as ordinary SQL. Consequences:

• a ; inside a heredoc body ends the statement: select $$a;b$$ parses to a single statement whose
  SQL is only select $$a, i.e. the rest of the query is silently dropped. Because
  ClickHouseConnectionImpl.prepareStatement builds the prepared query from parsedStmt.getSQL(),
  the driver then sends the truncated SQL to the server;
• a body character that is not a valid token in that position (?, an operator, ...) aborts the
  parse, so the statement is classified as UNKNOWN with no table name — e.g.
  select $$a?b$$, 1 from tbl and insert into tbl values ($$a;b$$, 1).

This is the v1 counterpart of #3029 / #3031 (the jdbc-v2 JavaCC and ANTLR4 grammars) and is a
separate mechanism from #3035 (the v1 JdbcParameterizedQuery placeholder scan) — both layers have
to know about heredocs for the v1 driver to accept such a statement.

Steps to reproduce

Parser level (main @ 1a11756):

ClickHouseSqlStatement[] stmts = ClickHouseSqlParser.parse("select $$a;b$$", new ClickHouseConfig());
stmts.length;            // 1
stmts[0].getSQL();       // "select $$a" -- expected "select $$a;b$$"

ClickHouseSqlParser.parse("select $$a?b$$, 1 from tbl", new ClickHouseConfig())[0]
    .getStatementType(); // UNKNOWN -- expected SELECT

Driver level, with the v1 driver (clickhouse.jdbc.v1=true):

conn.prepareStatement("select $$a;b$$ as s").executeQuery();
// Code: 62. DB::Exception: Syntax error: failed at position 8 ($): $$a.

The server accepts all of these statements — a heredoc is one string literal to it:

:) SELECT $$a;b$$, $tag$ x $tag$, $$a(b,c)$$
a;b      x      a(b,c)

Expected behaviour

A heredoc is lexed as a single string literal, so its body cannot split a statement or change its
classification.

Environment

• Client version: main @ 1a11756
• Language version: Java 8+
• ClickHouse server: 26.5.1.882 (server behaviour is not version-specific here)

Notes

clickhouse-jdbc (v1) is the legacy stack; close this if v1 grammar changes are out of scope.