initial work to support testing on windows CI bots

Prep for 0.4.0 release

* `resizeInputTensor`

* Replace use of asExternalTypedData with asTypedList.

* Update changelog and pubspec.yaml

This breaks the package in Dart 2.6.0-dev6 but allows us to land https://dart-review.googlesource.com/c/sdk/+/121422 by being able to pin the git hash of this commit in the DEPS file.

* Remove use of deprecated FFI features via package:ffi.

* Update pubspec.yaml

* Enable ci testing on osx

Significantly improve performance by using `asExternalTypedData`+`setRange` instead of `Pointer.store`

 Use Pointer.asExternalTypedData

This was created by running

`bazel build -s tensorflow/lite/experimental/c:libtensorflowlite_c.dll`

after renaming the .so target to have a .dll suffix.

This was created by running

`bazel build -s --config=darwin_x86_64
tensorflow/lite/experimental/c:libtensorflowlite_c.so`

on a MacBook.