This change adds additional Tonic templates for automatically generating bindings for Dart FFI, as well as serialisation of the bindings.
- Adds parallel FfiDispather templates to the existing DartDispatcher used for (old) native bindings.
- Adds serialisation of the bindings to enable automatic conversion and verification.
- Extends existing DartConverters with conversions to and from the FFI transport types.
- Adds new test (ffi_native_unittest.cc) for the above.
This will allow us to replace the existing native functions in e.g. dart:ui with new Dart FFI native functions.