Namerdart (#7187)

* Apply Namer to Dart.

- Also refactor idl_gen_dart a bit
  - to use more const and references
  - out parameters should be the last argument

* Add keyword test

* minor fixes

* fix merge

* extra 's'

* move dart keyord into dart dir

* Address comments

* Use $ for escaping keywords
* Outparameters for namespace_map

* Escape dollar in toString

* Escape dollar in toString2

* Use UpperCamelCase for types and variants

* try to fix ToString

* namer Type fixes

* Remove path prefixing in imports

* gen code

Co-authored-by: Casper Neo <cneo@google.com>

scripts/generate_code.py

@@ -363,6 +363,7 @@ flatc(
     prefix="nested_namespace_test",
     schema=glob(tests_path, "nested_namespace_test/nested_namespace_test*.fbs"),
 )
+flatc(BASE_OPTS + DART_OPTS, prefix="../dart/test/", schema="keyword_test.fbs")
 
 # Swift Tests
 swift_prefix = "FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests"