Reland "Re-land "Add a generic return type for js_util functions""

This reverts commit b70a134933d7678dbc91513d6e4691750961e111.

Reason for revert: google3 linter bugs disabled with a comment and Flutter PR with new js_util landed with ignore comments. Should be safe to reland.

Original change's description:
> Revert "Re-land "Add a generic return type for js_util functions""
>
> This reverts commit 66cbeb67188c69c340bcafd5f454608f693fea96.
>
> Reason for revert: Causes dart analyzer and dart linter to find
> issues within google3 and flutter, causing breakages and blocking
> the roll.
>
> Original change's description:
> > Re-land "Add a generic return type for js_util functions"
> >
> > This relands commit 46486cf260a7aee968514fa2eac44c361cfbf8ac.
> >
> > The differences from the original commit:
> >   - jsify is no longer being made generic
> >   - Updated the CHANGELOG
> >
> > Change-Id: Ibc3402833cce2babbec9a57ad73963d7b9442ed8
> > Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/216920
> > Commit-Queue: Riley Porter <rileyporter@google.com>
> > Reviewed-by: Sigmund Cherem <sigmund@google.com>
>
> TBR=sigmund@google.com,srujzs@google.com,rileyporter@google.com
>
> Change-Id: Ic2ff63bc9658ccafcab3db75bdd06814d2f17b76
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/216963
> Reviewed-by: Siva Annamalai <asiva@google.com>
> Commit-Queue: Siva Annamalai <asiva@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ia8c753b568b0aca10e7784126048bddd9e1ab976
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217148
Reviewed-by: Riley Porter <rileyporter@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Riley Porter <rileyporter@google.com>