A lot of this change is just documentation comments, but it includes some minor updates such as supporting "lazy" on variables.
All changes are backwards compatible and this should not affect any tests or functionality of Dart's DAP implementation (but provides the ability for us to use the new features).
Change-Id: Ief81927f2f370b4bfb6b5a9acc8659c45c33ea18
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310161
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>