FutureOr conditional expression typing issue

I'm running into a typing issue similar to dart-lang/sdk#28783, but in the context of a conditional expression (`?:`)
```dart
FutureOr routerCanDeactivate(next, prev) =>
someExpression
? true
: methodReturningFutureBool();
```
Under 1.22.1, this results in an analyzer warning:
> WARNING: Unsafe implicit cast from 'Object' to 'FutureOr'. This usually indicates that type information was lost and resulted in 'dynamic' and/or a place that will have a failure at runtime.

But the analyzer is happy if I put an explicit cast (which IMHO should be unnecessary):
```dart
FutureOr routerCanDeactivate(next, prev) =>
someExpression
? true as FutureOr // <================== cast
: methodReturningFutureBool();
```
@leafpetersen @bwilkerson @nex - I wasn't sure if you'd want a separate issue for this, or whether you'd prefer clumping it up with dart-lang/sdk#28783. It felt like `?:` might have its typing rules handled separately from if-then-else statements. Anyhow, I'll let you mark this as a dup if you want to merge the issues.

cc @kwalrath @matanlurey

Start with the conditional-expression example in the issue and reproduce the analyzer warning under the reported Dart version. Compare its typing behavior with the related dart-lang/sdk#28783 issue and the explicit-cast variant; done means the intended behavior and any required language or analyzer change are established.

Written by the indexing model from the issue text.