Upgrade SDK dependency to 2.12.0-0

[lrhn]

Also depend on package:convert 3.0.0-nullsafety.

[mit-mit]

What would it take to drop the dependency override on convert?

[mit-mit]

We should update the version (currently version: 2.2.0-nullsafety-dev) to use our recommended format, which I believe would be version: 3.0.0-nullsafety.0?

[lrhn]

I updated the version number to 3.0.0-nullsafety.0.
Now we need dep-overrides for many more packages (all of those directly or transitively depending on crypto <3.0.0)

[jakemac53]

@natebosch was assigned this package in the sheet so I would wait for his lgtm that this is ready to publish just to double check, otherwise we should leave the version at -nullsafety-dev (or maybe -nullsafety.0-dev?

[lrhn]

Definitely not ready to publish, so @natebosch, feel free to start from scratch or take over this attempt.

[jakemac53]

This could still land if we change the version to 2.2.0-nullsafety.0-dev in that case, bumping the sdk constraint LGTM

[mit-mit]

@natebosch @jakemac53 what's the story about the needed dependency override?

[natebosch]

what's the story about the needed dependency override?

They will be necessary for packages that are making breaking changes are are also circularly dependencies of anything in dev_dependencies like package:test. As long as we don't need overrides for stuff in dependencies it's still OK to publish, and we then can expand the constraints from things that depend on it and remove the override. It sometimes takes a bit of time, but it doesn't introduce much risk.