web: allow executing multiple statements

[stevenctl]

Adds a method that allows executing multiple statements from a single sql string.
See powersync-ja/sqlite_async.dart#123 and powersync-ja/sqlite_async.dart#122 for context.

Disclaimer: I have not taken the time to set up the test dependencies on my my machine yet.

[simolus3]

Thanks, I agree this functionality is a useful addition 👍

Implementation-wise, I think we can probably do this within the existing protocol. When running without parameters, CommonDatabase.execute will use sqlite3_exec which internally supports multiple statements.

Given that the worker already uses execute, I'd expect that calling execute on the client without parameters should accept multiple statements. Is that not what you were seeing?

[stevenctl]

Assuming the wrapper ends up using execute here, this PR is probably not needed. I made incorrect assumptions on why the wrapper chose select and prepareBatch. I'll close this for now.

And thanks for your quick response across all the issues/PRs.