chore(deps): update dependency google/protobuf.dart to v21

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
google/protobuf.dart	major	v20.0.1 -> v21.0.1

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Release Notes

google/protobuf.dart

### [`v21.0.1`](https://togithub.com/google/protobuf.dart/releases/tag/protoc_plugin-v21.0.1): protoc_plugin-21.0.1 [Compare Source](https://togithub.com/google/protobuf.dart/compare/protoc_plugin-v21.0.0...protoc_plugin-v21.0.1) - Fix missing protobuf import in generated grpc files. ([#​844]) [#​844]: https://togithub.com/google/protobuf.dart/issues/844 ### [`v21.0.0`](https://togithub.com/google/protobuf.dart/releases/tag/protoc_plugin-v21.0.0): protoc_plugin-21.0.0 [Compare Source](https://togithub.com/google/protobuf.dart/compare/protoc_plugin-v20.0.1...protoc_plugin-v21.0.0) - Identifiers `fromBuffer`, `fromJson`, `$_defaultFor`, `initByValue` are no longer reserved. Proto fields with those Dart names will no longer have a suffix added. ([#​679]) - Remove message constructor arguments. Constructors with arguments cause increase in release binary sizes even when no arguments are passed to the constructors. ([#​703]) **Migration:** Set the fields after construction, using cascade syntax. For example, if you have: ```dart MyMessage(a: 123, b: [1, 2, 3]) ``` You can do: ```dart MyMessage() ..a = 123 ..b.addAll([1, 2, 3]) ``` - Require Dart `2.19`. - Export public dependencies (`import public`s in proto files) in `.pbenum.dart` files, same as `.pb.dart` files. ([9aad6aa]) - Fix decoding map fields when key or value (or both) fields of a map entry is missing. ([#​719], [#​745]) - Generated files now split `ignore_for_file` comments across multiple lines when necessary. ([#​770]) - Generated files now uses shared consts to eliminate repeated `bool.fromEnvironment()` expressions. ([#​772]) - Removed accidental `///` at the top of generated Dart files to avoid new `dangling_library_doc_comments` lint. ([#​774]) - Generated files now have sorted imports and have fewer import-related `ignore_for_file:` analysis directives. ([#​778]) - Remove duplicated consts in generated files. ([#​773]) [#​679]: https://togithub.com/google/protobuf.dart/pull/679 [#​703]: https://togithub.com/google/protobuf.dart/pull/703 [9aad6aa]: https://togithub.com/google/protobuf.dart/commits/9aad6aa [#​719]: https://togithub.com/google/protobuf.dart/issues/719 [#​745]: https://togithub.com/google/protobuf.dart/pull/745 [#​770]: https://togithub.com/google/protobuf.dart/pull/770 [#​772]: https://togithub.com/google/protobuf.dart/pull/772 [#​773]: https://togithub.com/google/protobuf.dart/pull/773 [#​774]: https://togithub.com/google/protobuf.dart/pull/774 [#​778]: https://togithub.com/google/protobuf.dart/pull/778

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