Cast JSON objects to their expected type avoiding follow-on dyamic calls

[srawlins]

Work towards #6929. This is the big one.

This diff is unpleasant, with so many explicit casts. But this is what is required to avoid dynamic calls in this JSON-processing-heavy code. Feedback about whether we want dynamic-free, explicit cast code, as a requirement (like, guarded with a lint rule), is 100% welcome please let me know 😁 .

This diff is not too large (+75/-72 lines) but it touches a lot of files, and I'm happy to break it up, if that helps the review.

The new extension types should be a real alternative to casting JSON-parsed objects like this. They require Dart 3.3, so we can't land any yet (I think?). But as an example, let's look at the diff in logging_controller.dart. Instead of casting each value like entry['source'] as String?, we can type entry as an Extension Type called Entry:

extension type Entry(Map<String, Object?> data) {
  String? get source => data['source'];
  Map<String, Object?>? get displaySize => (data['displaySize'] as Map).cast<String, Object?>();
  Map<String, Object?>? get imageSize => (data['imageSize'] as Map).cast<String, Object?>();
}

Then all access on this object is restricted to the API declared above. If folks are OK with the code as is, and want to explore extension types later (soon), we could also kick the can down the road.

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[kenzieschmoll]

They require Dart 3.3, so we can't land any yet (I think?)

We can use these in the devtools_app and devtools_test packages. The flutter-candidate.txt file contains the Flutter version that the DevTools CI runs with.

[srawlins]

Oh cool! WDYT of extension types? I could send a proof-of-concept PR.

[kenzieschmoll]

Oh cool! WDYT of extension types? I could send a proof-of-concept PR.

Let's give it a go. I'm eager to see how these work in practice!

[kenzieschmoll]

@srawlins are you still planning on landing this? Or has the work here been landed in other PRs?

[srawlins]

It looks like basically everything in this PR landed in other PRs, as extension types and other fixes. Closing, thanks!!