The cargo target directory tree is now populated with a cmake package
file and that's also installed into the prefix specified with the cargo
cmake xtask.
As a consequence, the cpptest example can be built by first building the
cmake package:
cargo xtask cmake
or
cargo xtask cmake --release --target some-triplet)
or
cargo xtask cmake --release --prefix /somewhere --install
and then run cmake in the cpptest example with a prefix path:
-DCMAKE_PREFIX_PATH=/where/you/installed/it or simply
-DCMAKE_PREFIX_PATH=../../target/debug for example.
Pending still is the sixtyfps compiler tool installation and discovery.
This is done by calling cargo with json output to build the libraries,
collect the .a files, extract the native libraries needed for final
linkage and pass all that to a CMake project that cobbles together the
.a files into a propery cmake target with include paths, etc.
Remove the Optional from the evaluation context passing for property
evaluation. Unfortunately there are nullptr uses left on the C++ side,
that need to be replaced with passing through.
