feat(cppclient): provide entry points for C API

[kosak]

This PR provides the entry points for the "C API" to the Deephaven C++ library.

Notes for the reviewer: client_options_interop.[cc,h] is probably the easiest to understand so I would recommend starting there. Then client_interop.[cc,h]

In many cases this is just writing "glue code" mechanically just by looking at the signatures of the methods in the C++ classes.

In a few cases we have made exceptions for simplicity.

For example TableHandle::Sort takes a vector of SortPair. For the C API, we could take an array of SortPair objects. But I decided it was simpler to decompose the SortPair object into its three components: column_name_, direction_, and abs_. So, for the Sort() C API we just pass in three arrays: of column names, of directions, and of abs, plus their length. Then the C API doesn't need to define a "SortPair" object at all.

There is also a bunch of template-heavy code involving changes to TableMaker. The C# code relies on this heavily (to make temporary tables for use in tests). You may not need to drill into this code, because it is complicated.

Currently the C++ test code, such as in select_test.cc, uses a call to the templated CompareTables method to compare actual tables to expected tables. In a future PR I will modify all this code to use TableMaker instead. At that time it will probably be more obvious how TableMaker is used.