Add an additional C API example "aggregates_string" which demonstrates running min/max on string dimension and emitting coordinates from the same query

[rroelke]

An example like this would have been a useful reference when building the query aggregate API in tiledb-rs (and in fact it shows that we did a few things wrong over there).

So, we combine the quickstart_sparse_string.c and aggregates.c examples into a new example which demonstrates the above.

I have also added tiledb_examples.h with some functions/macros to do error checking. Whenever I have played with one of the examples to make a bug reproducer or learn a bit I am adding a bunch of error checks to see if I am doing anything wrong. Error checking should be a standard part of the examples and this header provides a fairly non-intrusive way to do it.

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TYPE: IMPROVEMENT
DESC: Add aggregates_string.c example and tiledb_examples.h for common example code

[teo-tsirpanis]

Thanks for working on this! Left some comments, and it might be a good idea to add a corresponding C++ example as well.

[teo-tsirpanis]

What is the purpose of min_offsets? Since Min(rows) is an aggregate it will have only one value and its size can be obtained through min_size set above, but I'm seeing min_offsets[0] being used below; shouldn't it always be zero?

If the Core requires an offsets buffer for a variable-sized aggregate field to be set, that should be fixed.

[rroelke]

That's right, the offsets will always be written as a single array whose contents are zero.

The offsets buffer is required.

Both of these aspects are also true if you were to query a single variable-length cell; while I agree that there's no data to be communicated, it has the same structure as existing code. So I'm not sure I agree with you that anything is worth changing here.

[KiterLuc]

+1 on adding the matching CPP API example.

[rroelke]

I have added a corresponding C++ example