Add [Dart] support (#4676)

* Add [Dart] support

* fix enum vectors

* Allow for opt out of string interning

* fix comment style, make interning opt in

* remove Offset<T>, prefer int

* avoid creating unnecessary vtable objects

* start work on tests - do not generate builder if struct has 0 fields - add int64

* support reading structs properly

* correctly handle reading vectors of structs, dartfmt

* support structs, fix unnecessary prepares

* fix bool customizations

* undo unintentional removal of file

* docs updates, complete tutorial, bug fix for codegen

* more documentation

* Update docs, add to doxygen file

* update package structure, add samples script/code

* rearrange sample

* Tests

* Add readme for pub

* cleanup package for pub

* update docs for renamed file

* remove custom matcher, use `closeTo` instead

* remove unintentional file

* remove unintended file checkin

* use auto, move method, cleanup

* refactor to ObjectBuilders, add Builders

* Update tests, examples

* Add files missing from previous commit

* documentation and example updates

* Update LICENSE, make dartanalyzer happy, fix minor bugs, get rid of duplicate files, publish script

* fix sample for slightly different schema

* Update pubspec.yaml

dart/pubspec.yaml

@@ -0,0 +1,18 @@
+name: flat_buffers
+version: 1.9.0
+description: >
+  FlatBuffers reading and writing library for Dart.  Use the flatc compiler to
+  generate Dart classes for a FlatBuffers schema, and this library to assist with
+  reading and writing the binary format.
+
+  Based on original work by Konstantin Scheglov and Paul Berry of the Dart SDK team.
+authors:
+- Dan Field <dfield@gmail.com>
+- Konstantin Scheglov
+- Paul Berry
+homepage: https://github.com/google/flatbuffers
+documentation: https://google.github.io/flatbuffers/index.html
+dev_dependencies:
+  test: ^0.12.33
+  test_reflective_loader: ^0.1.4
+  path: ^1.5.1