Respect upper bound of Flutter constraint in root packages after 3.9

[sigurdm]

Solves flutter/flutter#95472 (at least partially)

By making this depend on language version we avoid a breaking change

[sigurdm]

cc @mit-mit

[sigurdm]

@mit-mit whom in the flutter world should we inform, and should we make a breaking change announcement?

[mit-mit]

Yeah, I think we should do both a flutter breaking change and dart breaking change.

Also, should we consider a flag (e.g. dart|flutter pub get --ignore-upper) for those that need the current behavoir?

[sigurdm]

Also, should we consider a flag (e.g. dart|flutter pub get --ignore-upper) for those that need the current behavior?

Probably better with an env-var. It is hard to set the flag everywhere we resolve.

Even then it might be hard - dart run or the IDE might just resolve, it is hard to set the environment or add command-line arguments for the IDE.

[mit-mit]

I don't think folks are going to need it for everyday use (the breaking change process might help us understand if that is indeed the case), so I think that a flag on get and run for the occasional CI breakage might be sufficient?

[sigurdm]

Might be.. I still prefer it as an env-var, but I can live with both...

[sigurdm]

I realized by introducing the new interpretation based on language-version we can avoid making the change breaking!