[dart/ffi] C++ tuples, vectors, and exceptions

[dcharkes]

Creating an issue, so we have somewhere to point to every time this comes up. (I thought we already had an issue for this, but I cannot find it.)

C++'s std::tuple, std::vector, exceptions are not part of the ABI, and can be laid out differently in memory by different compilers.

At this time we are not considering adding interaction with these C++ constructs to dart:ffi.

The way to work with C++ features is to write a C wrapper around them.

/cc @sjindel-google