Fix string passing at interface C++ to JS

[carlopi]

Thanks to @jraymakers that identified the problem.

There are still a few places where we pass table names or DB names, those ought to be shorter, but I will address and remove those in a separate PR, for now keeping old and new interface in, but using only the new one where we pass only malloc-ed memory around.

[jraymakers]

Should createPrepared get the same treatment? It also takes a query string.

[carlopi]

Should createPrepared get the same treatment? It also takes a query string.

Yes, thanks. I will address those in a separate PR, I think this still makes sense as-is.

[jraymakers]

Should createPrepared get the same treatment? It also takes a query string.

Yes, thanks. I will address those in a separate PR, I think this still makes sense as-is.

Separate PR is fine. But note that createPrepared is also an important call for us.

[jraymakers]

Less important for us, but also needing attention, is getTableNames.

[jraymakers]

This is minor, but a couple of the C functions have unused "script" arguments:

• duckdb_web_pending_query_poll
• duckdb_web_pending_query_cancel

[carlopi]

Follow up is here: #1906