[image_picker] Upgrade mime to v2

[emersion]

We don't use extensionFromMime() so the breaking change doesn't impact us:
https://github.com/dart-lang/tools/blob/main/pkgs/mime/CHANGELOG.md#200

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[emersion]

Oh, contributing requires a CLA. Sorry, I do not wish to surrender my copyright.

[cbracken]

@emersion totally understandable.

I'm curious if the looser version constraint is causing a problem for you somewhere. If so, enough info for us to file an issue in the issue tracker would be enough to cause an existing contributor to jump out of the woodwork and bump the constraint to 2.0.0.

[emersion]

Good point, opened flutter/flutter#156905

[cbracken]

New patch out at #7879. Thanks for filing the issue. Also thanks for your work on several pieces of software I use daily.