* Dart - change Builder "lowFinish()" to "buffer" and "finish()" to not void return
Aligning the API with other languages, e.g. c++ and allowing custom use-cases to avoid creating a Uint8List
* Dart - change builder.buffer to check that finish() was already called
* Dart - builder - move !finished assertion to _prepare() which is run from all other functions
* dart test scripts - generate with `--gen-object-api`
* Dart object API, pack and unpack methods (WIP)
* Dart flatc - extract Builder code to separate functions to reuse it in Pack()
* Dart flatc - use builder field-building implementation in pack()
* Dart flatc - add pack() as an intance method of the "T" class
* Dart object API - make inner fields unpacked as well
* Dart object API - use pack() when collecting field offsets
* Dart object API - use packOnce() for fields that are structs or vectors of structs
* Dart object API - remove obsolete union support TODO
* Dart object API - minor review changes, test and fixes
* Dart object API - revert packOnce() - not supported by other object API implementations
* Dart object API - update docs
* update dart generated code in tests/ to fix CI failure on ./scripts/check-generated-code.sh
* Dart flatc - fix compilation for old MSVC and c++0x
Ivan Dlugos