Revert "[share] Migrate to null-safety"

[blasten]

flutter pub get is causing:

The current Dart SDK version is 2.12.0-125.0.dev.

Because shelf_static >=0.2.8 depends on mime ^0.9.0 and shelf_static >=0.1.0+1 <0.2.8 requires SDK version >=1.0.0 <2.0.0 or >=2.0.0-dev.55.0 <2.0.0, shelf_static >=0.1.0+1 requires mime ^0.9.0.
And because test >=1.16.0-nullsafety.7 depends on shelf_static ^0.2.6, test >=1.16.0-nullsafety.7 requires mime ^0.9.0.
So, because share depends on both mime ^1.0.0-nullsafety.0 and test ^1.16.0-nullsafety.13, version solving failed.

Unfortunately, there is a bug in the script, and the tests never ran. https://cirrus-ci.com/task/5395059044515840

Reverts #3311

[amirh]

lgtm

[mehmetf]

Normally, I would not suggest this.... however, could we attempt to forward fix rather than reverting? We are now back to tracking master in g3 and reverting back to non-null-safe code is going to complicate things a lot.

@blasten said the core reason is some of the package:test dependencies are not configured correctly even though package:test itself is migrated to null-safety so he is trying to fix it.

[amirh]

i think part of the reason is package shelf_static's nnbd version wasnt published. i pinged @kevmoo about it

[blasten]

dart-archive/shelf_static#45 fixes the issue momentarily

[kevmoo]

published latest shelf_static

[blasten]

Cool, thanks! flutter pub get works now.