Check for modern web libraries to determine if an app is a web app

[kenzieschmoll]

We currently check for the presence of dart:html in the connected app to determine whether it is a web application.

https://github.com/flutter/devtools/blob/master/packages/devtools_app_shared/lib/src/service/connected_app.dart#L88-L89

We should make this an OR check with a package:web or dart:js_interop library. Leaving the dart:html condition we allow us to still support apps using dart:html (e.g. g3).

[kenzieschmoll]

@kevmoo is package:web/web.dart the best library to check for? Is this guaranteed to be present in a Dart web app like dart:html used to be?

[kevmoo]

See https://api.dart.dev/

Everything rolls down to
dart:js_interop and dart:js_interop_unsafe

If you want to know if a library will only work with a "web" compiler (dart2js, dart2wasm) this is where to look.

You can likely borrow some logic from https://github.com/dart-lang/pana/

[kevmoo]

To be super clear: pkg:web is our BIGGEST example of the general rule: it rolls down to dart:js_interop and/or dart:js_interop_unsafe. Better to check for THOSE directly (er, indirectly via import/export chains).