[WIP] Add Dart support

[craiglabenz]

Begins adding pure-Dart support for MediaPipe.

TODOs:

• Add builder script to compile protos into Dart (found in dart_builder dir)
• (in progress) Add pure Dart wrapper around MediaPipe for TextClassification task
• Add other tasks
• Connect Dart wrapper to actual MediaPipe binaries
• CI/CD, copybara, etc

[charlieforward9]

I am trying to use TFLITE solutions in my Flutter project. I had a conversation with a Flutter expert indicating that the way Flutter works with the camera is sub-optimal, in short it creates copies from iOS -> Flutter -> etc... hogging resources and bogging performance.

With official Dart support, will we see optimized performance with the way inference is done using the camera plugin? Yes/No will suffice, just looking to learn about the roadmap a bit more. Thank you!