Emit a warning when a batch statement doesn't receive the right number of bind values

[lukaseder]

There are some use-cases when users do not pass the exact number of bind values to batch statements, and that can be OK, although it is not recommended. One use-case would be when users make use of named bind variables, and they don't want bind variables to change between batched statements.

When users use indexed bind variables, however, it is hard to make use of the above technique. In most cases, this is just an indication for a bug. We should emit a warning in the logs about this, when calling BatchBindStep.bind(...)

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See also: #3940