For loop variable type is dynamic when using null-coalescing operator about sdk

[Reprevise]

Closing as a duplicate of #54706

[eernstg]

Right, this is a duplicate.

Rule of thumb, just in case anyone reads this 😄 :

For an if-null expression e1 ?? e2, make sure there is no context type if you wish to transfer information from e1 to e2 during type inference ("don't disturb them"). Conversely, make sure there is a useful context type if you wish to provide information to both e1 and e2 "from the outside" during type inference.

The weird part here is that (chances ?? []) does have a context type when it occurs as the iterable of the for-in statement whose iteration variable does not have a type annotation, but it does not when it is the initializing expression of a local variable that doesn't have a type annotation. I created dart-lang/language#3696 to discuss that difference.

[eernstg]

PS: I closed dart-lang/language#3696. I no longer think that there is anything surprising or wrong about the observed behavior.