cli/sql: avoid ad-hoc parsing to match special input cases

[knz]

In #94408 we've introduced a regular expression in the SQL shell.
In commit fb09e01 we've introduced a mini-parser in the SQL shell go package.

Both of these things are architecturally incorrect -- we should have the server inspect the SQL syntax, as only the server has precise knowledge of the grammar that it recognizes.

There's a couple of solutions we can consider:

• lex and match the lexed tokens
• extend SHOW SYNTAX to reveals the token (using parser.Tokens()) in addition to the parsed syntax / errors

Jira issue: CRDB-24732

[otan]

we should have the server inspect the SQL syntax

i think i'm a bit hesitant to support needing a separate network call to inspect a syntax before executing it. i do think having a lightweight parser is a better option (or better yet the full parser).

lex and match the lexed tokens

on the server side? if it's the client side, is that what the "mini-parser" mentioned earlier?