UDF: fix sql prompt to handle multiline statements in`BEGIN ATOMIC...END` clause

[chengxiong-ruan]

Is your feature request related to a problem? Please describe.
Currently sql prompt would finish a statement and send it to back when it sees ; character outside of a string and hit Enter. This make it hard to write CREATE FUNCTION with BEGIN ATOMIC...END clause because the sql statements within the function body are not contained in a string and they all end with ;. For example:

CREATE FUNCTION f() RETURNS INT LANGUAGE SQL
BEGIN ATOMIC
SELECT 1;
SELECT 2;
END;

Currently sql prompt would finish early when it sees the first ; after SELECT 1 and we'd see a syntax error.

Describe the solution you'd like
We need to make sql prompt aware that it enters the BEGIN ATOMIC context and continue the multiline statement even it sees ; outside of a string. We could track the tokens sql seen so far to recognize the context.

Jira issue: CRDB-17401

[knz]

@dikshant epic CRDB-22182 is not the right epic for this issue. Please find it a new home. IT's a fully independent problem.