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
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