Add dart=3.10 pragmas to protobuf lib code

[osa1]

With this we can finally have the same formatting in the internal version and the open source version.

This also syncs some simple changes from internal to the open source.

With this the library code is almost identical internally and in the open source. There are still a few changes that need to be synced (enum names, reflection callbacks), which I'll do separately.

cl/832251175 adds the pragmas internally and reformats internal code. Also includes some trivial syncs from this version to the internal.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:protobuf	5.2.0	ready to publish	protobuf-v5.2.0
package:protoc_plugin	24.0.0	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[natebosch]

This is not safe to land. This breaks compatibility with older SDKs. It's troubling that we don't have CI set up to catch this.

We must either pin to language version 3.7 or change the constraint in the pubspec

environment:
  sdk: ^3.10.0

[osa1]

Why 3.7?

Why can't users who can't upgrade to 3.10 use the older version of the library?

The formatter in 3.9 doesn't respect the // @dart=... lines, that's why I waited until 3.10 to add these lines. We can add 3.7 as long as we always format with 3.10 or newer.

Why do you want to support 3.7 @natebosch?

You're right that if we have a min. supported version policy there should be checks to enforce it.

I've been maintaining this library for the past 3.5 years and I'm not aware of any such policy.