use dart_api

[rainyl]

Currently many native classes were wrapped with void *, which is not efficient for some classes, with dart_api we can create dart objects from native side directly, which can improve performance significantly, e.g., VecVecPoint -> List<List<Point>>

• https://github.com/dart-lang/sdk/blob/main/runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc

[rainyl]

Unnecessary, closed.